Process of conversion of biomass to fuel

ABSTRACT

The present invention is directed to processes for the direct conversion of lipidic biomass fuelstock to combustible fuels. In particular, the invention provides a process for the direct conversion of animal fats to transportations fuels suitable as replacement for petroleum-derived transportation fuels. In one embodiment, the method comprises the steps of hydrolyzing a lipidic biomass to form free fatty acids, catalytically deoxygenating the free fatty acids to form n-alkanes, and reforming at least a portion of the n-alkanes into a mixture of compounds in the correct chain length, conformations, and ratio to be useful transportation fuels. Particularly, the product prepared according to the invention comprises mixtures of hydrocarbon compounds selected from the group consisting of n-alkanes, isoalkanes, aromatics, cycloalkanes, and combinations thereof.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a Continuation of U.S. patent applicationSer. No. 12/897,318, filed Oct. 4, 2010, which is a Continuation of U.S.patent application Ser. No. 11/948,006, filed Nov. 30, 2007, whichissued as U.S. Pat. No. 7,816,570 on Oct. 19, 2010, which claimspriority to U.S. Provisional Patent Application No. 60/868,278 FiledDec. 1, 2006, and U.S. Provisional Patent Application No. 60/913,361Filed Apr. 23, 2007. All of the foregoing are incorporated herein byreference in their entireties.

FIELD OF THE INVENTION

The present invention is directed to processes for converting biomassinto fuel. More particularly, the processes of the invention allow forconversion of lipidic biomass sources into various hydrocarbons usefulas transportation fuels, particularly jet engine fuels, diesel enginefuels, and gasoline engine fuels.

BACKGROUND

Fossil fuels (or petroleum-based fuels) have formed the basis for energyproduction and transportation in the 20^(th) and 21^(st) centuries.Increased need among growing populations and emerging nations, as wellas market volatilities arising from wars, politics, and naturaldisasters, have focused world-wide attention on this non-renewableresource. In particular, rising costs and threats of shortages andsupply interruptions have recently highlighted the need for alternativefuel sources to petroleum-based products. Biofuels have particularlybeen a focus for alternative fuels.

Biofuel is generally regarded as being any fuel derived from biomass.The term biomass is often used in regard to plant-based sources, such ascorn, soy beans, flaxseed, rapeseed, sugar cane, and palm oil, but theterm can generally extend to any recently living organisms, or theirmetabolic byproducts, that play a part in the carbon cycle.

The production of biofuels to replace fossil fuels is in activedevelopment, focusing on the use of cheap organic matter (usuallycellulose, agricultural waste, and sewage waste) in the efficientproduction of liquid and gas biofuels which yield high net energy gain.Biofuels are viewed as environmentally favorable (particularly overfossil fuels) because the carbon in biofuels was recently extracted fromatmospheric carbon dioxide by growing plants, and burning the biofuelsdoes not result in a net increase of carbon dioxide in the Earth'satmosphere. Perhaps more importantly, biofuels are a renewable fuelsource, and the potentially limitless fuel supply derived therefrom canhave a stabilizing effect on fuel prices in the long-term.

One widespread use of biofuels is in home cooking and heating (e.g.,wood, charcoal, and dried dung). Biologically produced alcohols, mostcommonly methanol and ethanol, and to a lesser extent propanol andbutanol, can be produced through enzymatic and microbiologicalfermentation. For example, ethanol produced from sugar cane is widelyused as automotive fuel in Brazil, and ethanol produced from corn isbeing used as a fuel additive in the United States. Gases and oils arealso being produced from various waste sources. For example, thermaldepolymerization of waste materials (including plants, food, paper,plastic, paint, cotton, synthetic fabrics, sewage sludge, animal parts,and bacteria) allows for extraction of methane and other compoundssimilar to that obtainable from petroleum.

The need for alternative fuel sources, and particularly biofuels, alsoextends to high end uses, such as automobile and jet fuels. Almost allhigh end use fuels (such as jet engine fuel, diesel engine fuel, andgasoline engine fuel) are presently made from petroleum. Accordingly,such fuels are prepared through refining of crude oils. Refininggenerally encompasses three basic categories of activities: separation,upgrading, and conversion. During separation, feedstock (e.g., crudeoil) is separated into two or more components based on some physicalproperty, typically boiling point. The most common separation method isdistillation. Upgrading uses chemical reactions to improve productquality by removing unwanted compounds that impart undesirableproperties. For example, “sweetening” relates to removal of mercaptansand other organosulfur compounds, which are corrosive. Hydroprocessinguses hydrogen and a catalyst to remove reactive compounds, such asolefins, sulfur compounds, and nitrogen compounds. Clay treating removespolar compounds by passing the fuel stream over a bed of clay particles.Conversion fundamentally changes the molecular structure of thefeedstock, usually by cracking large molecules into small molecules(e.g., catalytic cracking and hydrocracking).

FIG. 1 provides a schematic layout of a modern, fully integratedrefinery for preparing various fuel types. As seen in FIG. 1, crude oilis fed to the distillation column where straight-run light and heavygasoline, kerosene, and diesel are separated at atmospheric pressure.The bottoms from the atmospheric column are vacuum distilled to obtaingas oils for fluid catalytic cracking (FCC) or hydrocracker feed.Previously, the vacuum residue might have been used as a low-value,high-sulfur fuel oil for onshore power generation or marine fuel. Toremain competitive today, however, refiners must collect as muchhigh-value product as possible from every barrel of crude, and vacuumresidue may now be sent to a residue conversion unit, such as a residuecracker, solvent extraction unit, or coker. These units produceadditional transportation fuels or gas oils, leaving an irreducibleminimum of residue or coke.

The jet fuel produced by a refinery may be all straight-run orhydroprocessed product, or it may be a blend of straight-run,hydroprocessed, and/or hydrocracked product. Small amounts of heavygasoline components also may be added. Straight-run kerosene fromlow-sulfur crude oil may meet all of the jet fuel specificationproperties. Straight-run kerosene, though, is normally upgraded bymercaptan oxidation, clay treating, or hydrotreating before it can besold as jet fuel. The refinery must blend the available streams to meetall performance, regulatory, economic, and inventory requirements.Sophisticated computer programs have been developed to optimize allaspects of refinery operation, including the final blending step. Therefiner really has only limited control over the detailed composition ofthe final jet fuel product. It is determined primarily by thecomposition of the crude oil feed, which is usually selected based onconsiderations of availability and cost. Moreover, the chemicalreactions that occur in the conversion process are not specific enoughto allow for much tailoring of the products.

The consumption of transportation fuels continues to grow worldwide,particularly in light of the rapidly growing need for transportation inemerging economies. For example, just the consumption of jet fuel in theUnited States increased from 32 million gallons per day in 1974 to 70million gallons per day in 1999. Although fuel needs are obviouslygrowing, the number of refineries has not kept up with the growing need.According to the National Petrochemicals and Refiners Association, thelast refinery built in the United States was completed in 1976. Between1999 and 2002, refining capacity in the United States rose only 3percent. Moreover, public perception and environmental concerns makebuilding new refineries more and more difficult. For example, a reportfrom the California Energy Commission notes that even though 10refineries representing 20% of the state's refining capacity were closedbetween 1985 and 1995, it is unlikely that new refineries will be builtin California. Accordingly, not only is there a need for increasedamounts of transportation fuels, there is also a need for alternativesources (to combat dwindling petroleum supplies and the vicissitudes ofthe crude oil market) and alternative methods of preparing fuels.

In its Broad Agency Announcement (BAA) 06-43 posted Jul. 5, 2006, theDefense Advanced Research Projects Agency (DARPA) Advanced TechnologyOffice (ATO) began soliciting proposals for biofuels to explore energyalternatives and fuel efficiency efforts to reduce reliance on oil topower its aircraft, ground vehicles, and non-nuclear ships. DARPA'sBAA06-43 particularly sought efforts to develop a process thatefficiently produces a surrogate for petroleum based military jet fuel(such as the current standard fuel, JP-8) from oil-rich crops producedby either agriculture or aquaculture (including but not limited toplants, algae, fungi, and bacteria) and which ultimately can be anaffordable alternative to petroleum-derived JP-8.

Biodiesel has been proposed as an alternative source for jet fuelproduction; however, current biodiesel alternative fuels are produced bytransesterification of triglycerides extracted from agricultural cropoils. Specifically, fats are reacted with alcohols and converted toalkyl esters (biodiesel) followed by conversion of biodiesel to jetfuel. The overall reaction is provided below in Formula (1),

CH₂(OCOR¹)CH(OCOR²)CH₂(OCOR³)+3ROH+(catalyst)→R¹OCOR+R²OCOR+R³OCOR+CH₂OHCHOHCH₂OH  (1)

wherein R¹, R², and R³ represent possibly distinct hydrocarbon chains.As seen in Formula (1), one molecule of triglyceride is combined withthree alcohol molecules to produce three molecules of biodiesel and onemolecule of glycerol. Thus, the transesterification reaction convertsthe triglyceride triester to three fatty acid alkyl monoesters. Thisprocess unacceptably yields a blend of methyl esters (biodiesel) that is25% lower in energy density than JP-8 and exhibits unacceptablecold-flow features at the lower extreme of the required JP-8 operatingregime (−47° C.). For example, kinetic viscosity at 40° C. of fuelprepared in this manner is in the range of 1.9 to 6.0 centistokes, butthe viscosity of an acceptable jet fuel should be in the range of about1.2 centistokes. Further, it is common for such fuels to have a freezingpoint in the range of about 0° C. Moreover, as feedstock cost is theprimary production cost driver in the preparation of jet fuel frombiomass, there has heretofore been no process for preparing jet fuelfrom biomass that is affordable and utilizes a suitably availablenecessary feedstock material.

There is likewise an increasing need and desire to establish viablealternative fuel sources for other transportation vehicles, particularlyautomobiles. Alternative fuels, as defined by the Energy Policy Act of1992 (EPAct), include ethanol, natural gas, propane, hydrogen,biodiesel, electricity, methanol, and p-series fuels. As previouslypointed out, biofuels represent a potentially limitless fuel supply thathas heretofore been virtually inaccessible. The ability to use biomassas a source for automobile fuels, such as gasoline or diesel, could notonly potentially provide lowered gasoline prices due to increased supplybut also lessen the demand for crude oil and stem the fear of waningreserves.

Vegetable oils, animal fats, and algae lipids can be converted to acombination of liquid and gaseous hydrocarbons by transesterification,deoxygenation, pyrolysis, and catalytic cracking processes. All of theseprocesses have been developed to varying degrees over the past 100years. To convert these fuelstocks into fuel, some combination of theseprocesses can be employed, and optimal combination is a function of boththe fuelstock and the desired properties of the fuel product. Thepresent invention provides a process for preparing fuel from biomass.

SUMMARY OF THE INVENTION

The present invention provides processes for the preparation ofbiofuels. In one aspect, the invention provides for the directconversion of biomass into fuel. In preferred embodiments, the inventiveprocesses provide for direct conversion of lipidic biomass intotransportation fuels, such as jet engine fuel, gasoline engine fuel, anddiesel engine fuel.

In one embodiment, the inventive process comprises the following steps:(A) performing thermal hydrolysis on a lipidic biomass to form a productstream comprising a free fatty acid and form a by-product streamcomprising glycerol; (B) performing catalytic deoxygenation on the freefatty acid stream to form a product stream comprising an n-alkane; and(C) performing one or more reforming steps on the n-alkane stream toform a product stream comprising a mixture of hydrocarbon compoundsselected from the group consisting of n-alkanes, isoalkanes, aromatics,and cycloalkanes. Preferably, after step (C), the hydrocarbon compoundsare in a combination and ratio necessary to form an overall compositionuseful as a transportation fuel.

One or more of the individual process steps of the invention can requirethe application of heat. Process heating can be a particularly costlyaspect of many processes. The present invention, however, can make useof reaction by-products for process heating. For example, in oneembodiment, the inventive process further comprises recovering at leasta portion of the glycerol stream from the hydrolysis step and using theglycerol as a fuel for producing at least a portion of the process heat.Since glycerol is an unavoidable by-product of the hydrolysis oftriglyceride-containing lipids, the glycerol forms a particularlycost-effective fuel source. It is only according to the presentinvention, though, that the use of glycerol as a process heating fuelhas been recognized.

In one embodiment of the invention, the thermal hydrolysis stepcomprises introducing the lipidic biomass into the bottom of a reactorcolumn, introducing water near the top of the reactor column, andheating the reactor. Preferably, the reactor is heated to a temperatureof about 220° C. to about 300° C. under a pressure sufficient to preventthe water in the reactor from flashing to steam.

The catalytic deoxygenation step of the inventive process can be carriedout in various embodiments. For example, in one embodiment, thecatalytic deoxygenation step comprises gas-phase deoxygenation. Inanother embodiment, the catalytic deoxygenation step comprisesliquid-phase catalytic deoxygenation carried out in a hydrocarbonsolvent. In both embodiments, the catalyst used is preferably a noblemetal, such as palladium. Deoxygenation can also proceed by multiplemechanisms. In one embodiment, deoxygenation comprises decarboxylation.In another embodiment, deoxygenation comprises decarbonylation.

In the liquid phase embodiment, the catalytic deoxygenation ispreferably carried out in a hydrocarbon solvent. In such embodiments,the present invention again provides a distinctive benefit. Inparticular, the present invention realizes the ability to recover aportion of the n-alkane stream formed in the catalytic deoxygenationstep. This recovered n-alkane stream can then be used as at least aportion of the hydrocarbon solvent in which the liquid phase catalyticdeoxygenation step is carried out. This is beneficial in that is negatesthe need for introducing a separate solvent, and it also negates theneed to add costly heat to bring the solvent up to the reactiontemperature and avoid slowing the reaction process.

Deoxygenation according to the present invention can particularly bedifferentiated from thermal decarboxylation. Specifically, in certainembodiments, catalytic deoxygenation is carried out at a temperature atwhich deoxygenation does not substantially proceed by thermal actionalone. Moreover, catalytic deoxygenation according to the presentinvention achieves a conversion rate that is not seen in thermaldecarboxylation, particularly when carried out at the reactiontemperatures used according to the present invention.

The reforming step of the inventive process can comprise a number ofseparate reactions. For example, in certain embodiments, reformingcomprises one or more steps selected from the group consisting ofhydroisomerization, hydrocracking, dehydrocyclization, andaromatization. In specific embodiments, reforming comprises the use of asolid catalyst, which preferentially comprises a metal functionalcomponent and, optionally, an acidic-functional component. In otherembodiments, reforming comprises the use of two or more differentcatalysts. Moreover, the separate reactions in the reforming step can becarried out in the same reactor or in different reactors. Accordingly,in one embodiment, reforming comprises a first reaction carried out in afirst reactor and at least a second reaction carried out in at least asecond, separate reactor. Thus, reforming can comprise separating then-alkane stream into two or more reforming streams and directing the twoor more reforming streams separately into the first reactor and the atleast second reactor. In still another embodiment, reforming comprises afirst reaction carried out in a first reactor, a second reaction carriedout in a second, separate reactor, and at least a third reaction carriedout in at least a third, separate reactor. Again, the n-alkane streamcan be separated into three or more reforming streams that areseparately directed into the three or more reactors. In otherembodiments, the reactors can be aligned in a series such that a firstreforming product stream is formed in the first reactor and proceedsinto the second reactor where a second reforming product stream isformed.

The invention is characterized by the ability to use a common feedstockand arrive at specific transportation fuels. In specific embodiments,this arises from the ability to reform the n-alkanes into a variety ofcompounds representative of the types of compounds which make up commontransportation fuels. The correct combination and ratio can be achievedduring the reactions of the reforming step such that the reformingproduct stream is already in the desired combination and ratio ofcompounds. The invention also encompasses embodiment, however, whereinmultiple product streams are recovered from the reforming process, andthe streams are combined to form the final product having the desiredcombination of hydrocarbon compounds in the desired ratio. In specificembodiments, the reforming product stream comprises hydrocarboncompounds in a combination and ratio necessary to form an overallcomposition useful as a jet engine fuel, a gasoline engine fuel, or adiesel engine fuel. Preferably, the overall composition formed issubstantially identical to the counterpart petroleum-derivedtransportation fuel. Further, it is preferential for the steps of theinventive process to be carried out separately and sequentially.

The present invention is also characterized by the ability to arrive atthe desired fuel in an energy efficient manner. Thus, in certainembodiments, the process of the invention exhibits an overall energyefficiency of at least about 75%. Energy efficiency can be calculated asthe lower heating value of the produced transportation fuel over the sumof the lower heating value of the process reactants and the total energyinput into the process.

The inventive process provides an affordable source of biofuels throughconversion of lipidic biomass, such as animal fats, vegetable oils, andalgae lipids. In particular, the low cost animal fat fuelstock overcomesthe primary production cost driver for biofuels. Biofuels preparedaccording to the invention are also compliant with specificationsgenerally required for particular types of fuels. For example, jet fuelprepared according to the invention is amenable to on-site fuelcharacterization and combustion testing to maximize iterative feedback.More particularly, jet fuel prepared according to the invention providesthe energy density and cold flow properties required for jet enginefuels, such as JP-8 (i.e., energy density >44 MJ/kg, and cold flow <−47°C.).

Another key benefit of the invention is the unique diversity provided bythe lipidic biomass feedstock. In specific embodiments, the lipidicbiomass feedstock comprises animal fats, which alone provide a feedstockof approximately 1.5 billion gallons/year in the U.S. However, thefeedstock is more diverse, and the invention can use any biomass sourcecomprising triglycerides (both agricultural or aquacultural). The use oflipidic biomass as a fuel feedstock is further beneficial in that it isgenerally independent from weather-related uncertainties that can plagueother biomass fuel sources, such as sugar cane, corn, and the like,which rely on conversion of carbohydrate-based biomass rather thanlipid-based biomass. The benefit of lipidic biomass feedstock furtherlies in the robustness of the fuelstock supply, with the much greatergeographic diversity of animal production providing greater securityagainst strategic fuelstock sabotage, relative insensitivity to weatherpattern changes, and lower susceptibility to crop failure due to diseaseor infestations. In other words, geographical variations in lipidicbiomass prices can be overcome since the fuel production process can betailored to accommodate a cheaper biomass source in a given location.Thus, it is clear that the process of the present invention is usefulfor successfully producing a transportation fuel from a lipidic biomassfeedstock wherein the fuel meets all physical and chemical requirementsof the particular fuel while also providing an optimal efficiency andscalability.

DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a schematic representation of a typical modern refiningprocess for the preparation of fuels from crude oil;

FIG. 2 is a flowchart illustrating the steps for direct conversion oflipidic biomass to a transportation fuel according to one embodiment ofthe invention;

FIG. 3 is a graph showing the free fatty acid conversion product ofcanola oil after undergoing thermal hydrolysis according to oneembodiment of the invention;

FIG. 4 is a flowchart illustrating a summary of possible chemicalpathways for changing C₁₈ fatty acids into fuels;

FIG. 5 is a graph illustrating the difference between uncatalyzeddeoxygenation of stearic acid and catalyzed deoxygenation of stearicacid according to one embodiment of the invention;

FIG. 6 is a graph showing the n-alkane conversion product of stearicacid after undergoing catalytic deoxygenation according to oneembodiment of the invention;

FIG. 7 is a graph showing the total conversion products of stearic acidafter undergoing catalytic deoxygenation according to another embodimentof the invention;

FIG. 8 is a MS graph of the products representing the aromatic peakshown in the graph of FIG. 7;

FIG. 9 is a GC/MS chromatogram of the reaction product of deoxygenationof stearic acid carried out according to one embodiment of theinvention;

FIG. 10 is a graph showing the deoxygenation kinetics of stearic acidand oleic acids in H₂ according to one embodiment of the invention;

FIG. 11 is a schematic of a typical isomerization/hydrocracking network;

FIG. 12 is a chromatogram showing the reaction products after threehours reaction time in a reforming process according to one embodimentof the invention;

FIG. 13 is a GC-MS chromatogram showing the reaction products of areforming process according to another embodiment of the invention;

FIG. 14 is a graph showing the carbon number distribution of a gasolinefuel obtained after one hour of batch hydrotreating according to onereforming embodiment of the invention in comparison to the distributionof a typical regular unleaded gasoline; and

FIG. 15 is process flow according to one embodiment of the inventionshowing each process step.

DETAILED DESCRIPTION

The invention now will be described more fully hereinafter throughreference to various embodiments, and particularly in regard to theattached figures. These embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art. Indeed, the invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. As used in the specification, and in the appended claims,the singular forms “a”, “an”, “the”, include plural referents unless thecontext clearly dictates otherwise.

The present invention provides a process for the preparation of biofuelsvia direct conversion of biomass feedstock. The term “biofuel” as usedherein is understood to mean a composition derived from a non-petroleumbiomass and comprised of a mixture of hydrocarbons in the correct chainlengths, chain conformations, and compound ratios to be used as atransportation fuel. A “transportation fuel” as used herein isunderstood to mean a composition useful as a fuel in internal combustionengines, such as commonly found in transportation vehicles (e.g.,automobiles, airplanes, trains, and heavy machinery), the compositionincluding, but not limited to, a composition classifiable as a jetengine fuel, a diesel engine fuel, or a gasoline engine fuel.

The inventive process is characterized by feedstock flexibility, highprocess efficiency, effective utilization of process by-products, andthe ability to deliver a biofuel that is substantially identical to apetroleum-derived fuel product. In other words, the biofuel is formed ofclasses of compounds in the same ratios necessary to effectivelyfunction in the same manner as the petroleum-derived furl. In theprocess of the present invention, triglycerides can be converted to freefatty acids (FFAs) by hydrolysis and the glycerol byproduct andunreacted water can be separated, so that the first step in themulti-step process yields only FFAs for use in further process steps.The FFAs can then be decarboxylated/deoxygenated in a catalytic processto produce the n-alkane corresponding to the FFA alkyl tail group.Finally, the resulting mixture of alkanes (and alkenes) can behydroisomerized/hydrocracked to produce a mixture of isoalkanes (i.e.,branched alkanes) and n-alkanes. The mixture can further beisomerized/aromatized to form aromatics, such as toluene andnaphthalenes, or cyclized to form cycloalkanes.

The present invention particularly allows for the direct conversion ofoils with high free fatty acid content into a blend of hydrocarboncompounds useful as fuels, including jet fuel, diesel, and gasoline.Oils from feedstocks, such as agricultural crops (e.g., soybean oil,canola oil, and palm oil), aquacultural crops (e.g., algae), energycrops, animal fats, and waste grease, can be converted to a combinationof liquid and gaseous hydrocarbons by various chemical mechanismsincluding transesterification, deoxygenation, pyrolysis, and catalyticcracking, which processes have been developed to varying degrees.However, to prepare a useful fuel, such as gasoline, diesel, or jetfuel, it is not possible to simply pick and choose from among knownchemical processes. In other words, the mere existence of such processesdoes not lead to an overall process for preparing a useful fuel. Rather,it is necessary to employ an exact combination of processes in an exactorder under specific conditions, and the present process is inventive inpart because of the ability to recognize the exact combination ofprocess steps and the exact reaction parameters useful to take a commonlipidic biomass feedstock and convert it into the desired fuel product,whether it be gasoline, diesel, jet fuel, or another combustible fuelformed of a specific combination of hydrocarbons.

Since there is a tremendous investment in the current transportationfuels infrastructure, for any fuel to gain mass market penetration, itmust be compatible with the existing infrastructure. The biofuelsproduced according to the process of the present invention are virtuallyidentical chemically and physically to their counterpartpetroleum-derived fuels, thus making their introduction into the fuelsmarket seamless. This is highly advantageous over current fuelalternatives (e.g., the gasoline alternative ethanol), which requireengine modification for substantial use, and which can also requirespecial handling. For example, ethanol must be transported todistribution points by special carrier because of ethanol's hygroscopicnature and tendency to absorb water. Providing fuel from a renewablebiomass according to the present invention does not requireestablishment of a new distribution network, such as would be necessarywith fuel alternatives, such as ethanol, hydrogen, and the like. Rather,fuel prepared according to the invention can be directly introduced intothe existing distribution network and commingled with petroleum-derivedfuel.

Biofuels prepared according to the present invention also can becustomized to provide desirable qualities, particularly taking intoaccount the above factors that must be considered in preparing aspecific fuel type. For example, jet fuel (Jet-A, Jet A-1, and JP-8) isa middle distillate fraction that contains a mixture of straight andbranched chain alkanes, aromatics, and cycloalkanes. Carbon chainlengths of 10 to 14 are typical. Petroleum-derived jet fuels containapproximately 20% aromatics by volume, and these species contributedirectly to the production of particular matter in the exhaust and anideal jet fuel would have lower aromatic content. However, due to theelastomer seals in the jet engines, aromatics in the fuel are necessaryto prevent the seals from shrinking, thereby causing fuel leaks.Further, high energy density (by weight) and good cold-flow propertiesare critical for jet fuels.

Diesel fuel is composed primarily of C₁₀-C₂₀ hydrocarbons. A diesel fuelis characterized principally by its Cetane Index, which is a measure ofthe fuel's propensity to auto-ignite on compression. Normal hexadecane(cetane) is assigned a Cetane Index of 100, and branched alkanes andaromatic compounds have lower Cetane Indices. To improve cold flowproperties, as required for an all-weather diesel fuel, a trade-off ismade in Cetane Index by introducing some branched alkanes. A typicalCetane Index for petroleum diesel is around 50.

Gasoline is comprised mainly of C₅-C₁₂ alkanes, isoalkanes, andaromatics. Gasoline is characterized by Octane Number, which is ameasure of the fuel's propensity to resist auto-ignition on compression(and hence fuels with high Octane Numbers have low Cetane Indices).Branched alkanes and aromatics have higher Octane Numbers than normal(linear) alkanes. For example, iso-octane (2,2,4-trimethylpentane) hasan Octane Number of 100, whereas n-octane has an Octane Number of 0.

In a specific embodiment, a jet fuel can be prepared to match thechemical kinetics of Jet-A/JP-8 fuel comprising a dominant isoalkanecomposition and that provides an energy density of >44 kJ/kg, producesless soot than petroleum-derived JP-8, and has equivalent or improvedlow-temperature viscosity in relation to JP-8. One example of a chemicalkinetic surrogate for JP-8 is shown Table 1. A jet fuel matching thephysical properties of JP-8 would be expected to have a similarcomposition (i.e., similar ratios of n-alkanes, iso-alkanes, cyclics,and aromatics).

TABLE 1 Compound Wt. % n-dodecane 43% iso-cetane 27% methylcyclohexane15% 1-methylnaphthalene 15%Further, Table 2 summarizes the ability of the process of the presentinvention, in one embodiment, to provide a JP-8 fuel that meets orexceeds the performance required according to U.S. militaryspecifications.

TABLE 2 U.S. Military Jet Fuel Prepared by JP-8 Fuel PropertySpecification Inventive Process Energy density >42.8 MJ/kg 44.0 MJ/kg(gravimetric) Flash point >38° C. 42° C. Freezing point <−47° C. −48° C.Low-temp viscosity <8.0 centistokes 4.5 centistokes (−20° C.) Aromaticcontent <25.0 vol. % app. 8% Hydrogen content >13.4 wt. % 14.7% Densityat 15° C. 0.775-0.840 kg/L app. 0.8 kg/L Smoke point >25.0 mm >25.0 mmSulfur, total mass % <0.3% app. 0%

In further embodiments, the biofuels prepared according to the inventionalso include a desirable content of aromatics and cycloalkanes to meetall jet fuel properties (such as energy density, combustion quality,low-temperature fluidity, reduced volatility, and kinetic properties,e.g., carbon:hydrogen ratio and flame speed). Chemical kineticproperties of the fuel are very important, and the process of theinvention particularly allows for in-house jet engine testing that canlead to optimal distribution of jet fuel components, such as n-alkanes,isoalkanes, cycloalkanes, and naphthenes.

The process of the invention comprises three consecutive steps: (1)thermal hydrolysis of triglycerides (such as present in a lipidicbiomass feedstock) to produce free fatty acids; (2) catalyticdeoxygenation (e.g., decarboxylation) of the FFAs from step (1) to formn-alkanes; and (3) reforming of the n-alkanes from step (2) to producethe desired product distribution. These process steps are summarized bythe flowchart provided in FIG. 2.

In step (1), hydrolytic conversion of triglycerides (TG) to free fattyacids, a triglyceride-containing biomass feedstock is heated in thepresence of water to sever the bonds in the triglyceride moleculebetween the fatty acid chains and the glycerol backbone. This stepgenerally results in a product mixture of FFAs and glycerol (GL). Theoverall reaction for this process step is shown in Formula (2).

TG+3H₂O→3FFA+GL  (2)

where TG represents triglyceride and FFA represents free fatty acids.The initial hydrolysis reaction allows for accommodation of a broadarray of lipidic feedstocks.

In step (2), catalytic deoxygenation of free fatty acids to theircorresponding alkanes, the FFAs are specifically reacted in the presenceof a catalyst. As described below in more detail, deoxygenation canproceed by decarboxylation or decarbonylation (although decarboxylationis typically the main reaction pathway. The overall reaction for adecarboxylation process is provided in Formula (3).

FFA→n-alkane+CO₂  (3)

This process step can occur in a hydrocarbon solvent, and the presentinvention is particularly characterized in that the n-alkanes preparedcan be recycled as the solvent to maximize thermodynamic efficiency.Gas-phase deoxygenation (i.e., solvent-free) can also be used. Thecatalytic deoxygenation reaction parameters can be designed to providethe additional benefit of partial dehydrogenation. This can beparticularly useful to form a desired amount of unsaturated hydrocarbons(e.g., alkenes).

In step (3), the n-alkanes undergo reforming, such as byhydroisomerization/hydrocracking (HI/HC) and aromatization, to produce abiofuel comprising the desired mixture of isoalkanes, n-alkanes,aromatics, and cycloalkanes. Reforming can be accomplished in acontinuous flow stirred reactor, preferentially using a catalyst. Theoverall reaction for this step is provided in Formula (4).

n-alkanes isoalkanes+n-alkanes  (4)

The reforming step can be adjusted as needed to produce the propermixture of isoalkanes, n-alkanes, aromatics, and cycloalkanes to achievethe necessary physical, chemical, kinetic, and material interactionproperties useful in the desired fuel product. In certain embodiments,the reforming steps are adjusted to produce a mixture of hydrocarbonswherein the majority are isoalkanes (e.g., greater than about 50% byweight, greater than about 60% by weight, greater than about 70% byweight, or greater than about 75% by weight, based on the overall weightof the hydrocarbon mixture).

The present invention particularly arises from the identification of thespecific steps useful to sequentially transform a lipid into acombination of hydrocarbon compounds in the correct chain lengths,correct chain conformations, and correct ratios to provide a usefulbiofuel, such as biogasoline, biodiesel, or bio-jet fuel. Others haveattempted to transform oils into fuels, but such previous attempts donot achieve the controlled efficiency and reproducibility of the presentinvention. For example, by separately performing deoxygenation andreforming according to the present invention it is possible to optimizethe different catalysts used in the individual steps and thereby providethe necessary increased yield of isoalkanes in the C₇-C₁₄ range to formspecific fuel types. Moreover, by performing the catalytic deoxygenationis a separate step, it is possible to provide an oxygenate-freehydrocarbon stream that can be reformed to produce a broad range ofbio-based transportation fuels, including gasoline, diesel, and jetfuel.

The present invention is further beneficial in that by adjusting thereaction conditions

(such as by increasing reaction temperatures and lowering hydrogenpressures), the process can be optimized to favor the formation of ringstructures. For example, in certain embodiments, the process parameterscan be controlled such that the biofuel produced from the conversion ofthe biomass feedstock includes the correct proportions of aromatics andnaphthenes to match the kinetic parameters of petroleum JP-8. Such anoptimized process step is shown in Formula (5).

n-alkanes→isoalkanes+aromatics+naphthenes  (5)

In other embodiments, the process parameters can be controlled such thatthe biofuel produced includes the correct proportions of isoalkanes andaromatics, particularly C₈ isoalkanes, to match the kinetic parametersof standard gasoline. Such an optimized process step is shown below inFormula (6).

C₁₅₋₁₇ alkanes→C₈ isoalkanes+aromatics  (6)

The inventive process is further characterized in that it can beoptimized to utilize reaction by-products. For example, as noted above,the n-alkanes prepared according to Formula (3) above can be recycled asthe hydrocarbon solvent in liquid phase embodiments of the deoxygenationstep. Furthermore, the glycerol prepared according to Formula (2) abovecan be used as a thermal source for the above reactions. Combustion ofglycerol can be according to Formula (7) below.

C₃H₅(OH)₃+3.5O₂→3CO₂+4H₂O  (7)

Biomass Feedstock

The process according to the present invention utilizes biomass as astarting material and directly converts the biomass to a combustiblefuel. The term “biomass”, as used herein, means living and recentlyliving biological material, or their metabolic byproducts, that play apart in the carbon cycle. Biomass as used in the present invention ispreferably derived from renewable sources and, as such, typicallyexcludes commonly recognized fossil fuels (such as crude oil, naturalgas, and coal). While such fossil fuels are preferably not used asbiomass in the present invention, in certain embodiments, the biomassused in the inventive process can include a minor percentage ofcompounds directly recognized as fossil fuels, or derivatives thereof.

Preferentially, the biomass used as a fuelstock in the present inventioncomprises lipidic biomass. The term “lipid” generally refers tocompounds that are relatively insoluble in water and generally solublein nonpolar organic solvents. As used herein, lipids include fats,waxes, oils, and related and derived compounds. More specifically,lipids include monoglycerides, diglycerides, triglycerides, terpenes,phospholipids, fatty alcohols, sterols, fatty acids, and fatty acidesters. Thus, “lipidic biomass” according to the invention includes anybiomass having a content of lipidic material. Preferably, lipidicbiomass comprises material wherein a majority of the content, or theentire content, of the material comprises lipids.

In preferred embodiments, the lipidic biomass used in the invention isselected from the group consisting of vegetable oils, animal fats, andalgae lipids. Generally, any material, though, subject to formation offree fatty acids via hydrolytic reactions can be used in the inventiveprocess. Moreover, any material providing a source of triglycerides canbe used in the invention.

Soybean oil has received much attention as an abundant oil bearing crop,although more than 350 oil bearing crops have been identified to date,and any such vegetable oil, seed oil, or nut oil could be used in theinvention. In addition to these existing oil crops, other lipidicbiomass sources useful in the invention include algae and otheraquaculture crops, as well as strategic crops (such as cuphea),bacterial crops, and animal fats. This broad range of useful feedmaterials is beneficial because it allows for the use of the cheapestand most readily available feedstock at any given time or location.Accordingly, the process of the invention can be utilized in a varietyof locations and is not limited to a ready availability of a specificfeedstock.

Particularly advantageous for use according to the invention are animalfats, which generally contain a combination of saturated and unsaturatedcarboxylic acids, especially C₁₆ and C₁₈ carboxylic acids, and suchanimal fats have a number of advantages over vegetable oils. Inparticular, animal fats are generally cheaper than vegetable oils.Examples of animal fats that can be used in the invention include beeffat (tallow), hog fat (lard), turkey fat, and chicken fat, as well asany other vegetable oil or lipid. Lipidic biomass sources providing amajority of C₁₆ and C₁₈ carboxylic acids are particularly useful in thepreparation of jet fuels, as the inventive process is particularlyuseful for converting such starting materials to the C₁₀-C₁₄ compoundstypically present in jet fuels and other kerosene-type fuels. Similarly,biomass sources providing a majority of C₁₅-C₁₇ carboxylic acids areparticularly useful in the preparation of gasoline since the inventiveprocess, in specific embodiments, is particularly useful for convertingsuch starting materials to a majority of compounds in the C₈ range, suchas typically present in gasoline. Furthermore, the inventive process canadvantageously make use of waste vegetable oils as fuelstock.

The use of lipidic biomass as a fuelstock in the present invention alsoallows for a diversity of sources, which limits shortages and decreasesregional effects, such as weather. Moreover, the process can actuallyfunction to recycle waste materials. The process is not limited to theuse of virgin materials. Rather, the lipidic biomass can compriserecycled fats, oils, and other lipids as well. For example, cooking fatsand greases used in restaurants and fast-food chains can be a source offuelstock in the present invention. Still further, the present inventionprovides an alternative to disposal of animal fats from large-scale meatproduction facilities. Tyson Foods, for example, reported in 2006 thatit produces 2.3 billion pounds of animal fat per year. Moreover,vegetable oils are available in an amount of approximately 5 billiongallons per year. Thus, the lipidic biomass used as a fuelstock in thepresent invention can take on a diversity of forms and sources that canprovide a constant supply biofuel through the direct conversion processof the invention.

The fatty acid composition of fats and oils depends on the source. Sincethese are natural products, there is a range of typical compositionsencountered, as shown below in Table 3, which provides the fatty acidcontent of some common fats and oils.

TABLE 3 Saturated wt. % Mono-unsaturated wt. % Poly-unsaturated wt. %Fat/Oil C₁₂ C₁₄ C₁₆ C₁₈ >C₁₈ <C₁₆ C₁₆ C₁₈ >C₁₈ C₁₈ (2)^(a) C₁₈ (3)^(b)Soybean 0.3  7-11 2-5  1-3 0-1 22-34 50-60 2-10 Corn 0-2  8-10 1-4 1-230-50 0-2 34-56 Tallow 0.2 2-3 25-30 21-26 0.4-1 0.5 2-3 39-42 0.3 2Lard 1   25-30 12-16 0.2 2-5 41-51 2-3 3-8 ^(a)Linoleic acid;^(b)Linolenic acidThe present invention is particularly beneficial in that it accommodatesthe use of any of the types of feedstocks represented in Table 3,regardless of the differing fatty acid contents.

In certain embodiments, it is useful for the lipidic biomass to undergoone or more process steps prior to entry into the fuel productionprocess described below. Such additional process steps can be directlyincluded into the process of the invention (i.e., could be inserted intoa continuous process described herein immediately upstream of thehydrolysis step). In other embodiments, additional processing of thebiomass can take place separately from the process of the presentinvention.

In one embodiment, it is useful to degum the lipidic biomass,particularly when the lipidic biomass comprises a vegetable oil, such assoybean oil. The mucilage substances in plant oils consist primarily ofmixtures of phosphatides, with the amount and composition beingdependent on the type of oil seed and the method of obtaining the oil.The great majority of phosphatides can be separated from their micellarsolutions by means of hydratization, and used for obtaining lecithin.This process is referred to as wet degumming. A small portion ofphosphatides is not hydratizable and remains in the oil. The chemicalnature of these “non-hydratizable phosphatides” (NHP) is not completelyclear, however, studies have shown that they consist of calcium andmagnesium salts of phosphatide acids, in a proportion of more than 50%(see Hermann Pardun, Die Pflanzenlecithine [Plant lecithins], Verlag furchem. Industrie H. Ziolkowsky K G, Augsburg, 1988, page 181). The goalof conventional technical degumming processes is to remove thenon-hydratizable phosphatides from the oil to the greatest extentpossible.

Examples of degumming processes include the “Superdegumming process” andthe “Unidegumming” process of the Unilever company, the “Total Degumming(“TOP”) process” of the Vandemoortele Company, the “Alcon process” ofthe Lurgi company, and the “UF process” of the company KruppMaschinentechnik GmbH. In many instances, traditional aqueous degummingfor removing hydratizable phosphatides is integrated into theseprocesses, or precedes them. Degumming can particularly comprise asingle stage acid treatment (e.g., using phosphoric or citric acid) anda single stage hot water treatment followed by continuous removal of thehydrated gums in a degumming super centrifuge. See, for example, U.S.Pat. No. 4,698,185, which is incorporated herein by reference. Degummingcan also proceed by enzymatic processes, such as described in U.S. Pat.No. 6,001,640, which is incorporated herein by reference.

Hydrolysis of Lipidic Biomass

The lipidic biomass used in the process of the invention is firstsubjected to a hydrolytic conversion process to form free fatty acids.The lipidic biomass used in the invention, and particularly animal fats,can vary over a wide range in purity and quality. Further, many fatsources contain water and are mixtures of fatty acids, fatty alcohols,and fatty-acid esters. The process of the invention takes into accountthe diversity in the lipidic biomass fuelstocks and handles thisvariation in fat composition and quality by using a first stage fatsplitting process to produce high quality fatty acids which thenconstitute the main feed for downstream stages. This first stage fatsplitting process has the added benefit of simultaneously producing afuel source to drive the overall process of the invention. As furtherdescribed below, the glycerol produced in the hydrolysis step can berecovered and used as a combustible heat source. The flowchart of FIG. 2illustrates the removal of glycerol from this step and transfer into aglycerol burner, which provides the heat needed to at least partiallydrive the reactions of the invention.

Processes of fat splitting have been described in the art and are wellestablished in the fatty acid industry. See Sonntag, N. O. V., “FatSplitting”, J AOCS 56:A729-A732 (1979), which is incorporated herein inits entirety. Examples of fat splitting processes include the following:a) the Twitchell process developed in 1898, which involves atmosphericboiling of fat in the presence of various reagents; b) medium pressureautoclave splitting with a catalyst, such as ZnO; c) low pressuresplitting in the presence of a catalyst using superheated steam tointeract with oil in a tube type reactor; d) continuous, high pressureuncatalyzed countercurrent splitting; and e) enzymatic fat splitting.More recently, studies have demonstrated fat splitting by waterhydrolysis using temperatures in the range of 250° C. and water in thesubcritical state at pressures of 5 to 20 MPa and reaction times ofapproximately 20 minutes. See Kusdiana, D., and Saka, S. “Catalyticeffect of metal reactor in transesterification of vegetable oil,” J AOCS81:103-104 (2004), which is incorporated herein by reference. Thissubcritical process can be carried out in either batch mode or in acontinuous reactor, but large amounts of excess water are typicallyrequired to drive the reversible hydrolysis reaction to completion. Foroils, such as rapeseed oil, the water-to-oil molar ratio can be up toapproximately 217:1 (a volume ratio of approximately 4:1). The aqueousphase and the fatty acids come off in liquid form and can be separated.

In a particular embodiment, the continuous, high-pressure, uncatalyzedcountercurrent splitting process is used employing a reaction tower orcolumn. This fat splitting process is particularly characterized by hightemperatures and high pressures and continuous removal of liberatedglycerol with a water stream. This process is particularly efficient andinexpensive for large scale production of saturated fatty acids fromfats and oils.

Countercurrent splitting is particularly advantageous in that it ispossible to approach complete reaction without the use of excessiveamounts of water. To achieve this result, it is beneficial to maintain aresidence time in the reactor of about 1 hour to about 4 hours, about1.5 hours to about 3.5 hours, about 1.5 hours to about 3 hours, about1.5 to about 2.5 hours, or about 2 hours at the reaction temperature. Inlight of the residence time, it is possible to use reaction temperatureson the lower end of the preferred temperature scale. For example, incertain embodiments, countercurrent splitting can be carried out at atemperature of about 240° C. to about 260° C., about 245° C. to about255° C., or about 250° C.

In other embodiments, it is possible to carry out the hydrolysis in aquasi-batch mode. Such embodiments are beneficial in that residence timein the reactor can be greatly reduced. Preferably, such embodiments arecarried out at reaction temperatures on the higher end of the preferredtemperature scale. For example, in certain embodiments, the quasi-batchhydrolysis can be carried out at a temperature of about 270° C. to about290° C., about 275° C. to about 285° C., or about 280° C. Under suchconditions, reaction time can be reduced to less than about 1 hour, lessthan about 45 minutes, or less than about 30 minutes. Preferably thereaction time is about 5 minutes to about 30 minutes, about 10 minutesto about 20 minutes, or about 10 minutes to about 15 minutes.

When using the quasi-batch process, it is useful to use a water-to-oilvolume ratio that is somewhat greater than required in thecountercurrent process. In the quasi-batch process, it is useful for theratio to be about 3:1 to 1.5:1, about 2.5:1 to about 2:1, or about 2.3:1v/v (water:oil). In the countercurrent process, however, thewater-to-oil ratio is preferably less than about 1.5:1, more preferablyless than about 1.25:1, even more preferably less than or equal to about1:1 v/v (water:oil).

It is also possible, according to the invention, to combine the abovemethods to provide an optimized process. For example, the reaction canbe carried out in a continuous, countercurrent process at a temperaturemore typically used in the quasi-batch process (e.g., about 280° C.). Insuch an embodiment, it possible to provide continuous processing with aresidence time on the order of about 10 minutes to about 20 minutes,preferably about 10 minutes to about 30 minutes.

In one embodiment, the fat is introduced by a sparge ring from thebottom of the reactor column with a high pressure feed pump. Water isintroduced near the top of the column, and the mass flow rate of thewater is preferably in the range of about 25% to about 75% of the massflow rate of the fat being introduced at the bottom of the column. Morepreferably, the water flow rate is about 30% to about 60% or about 40%to about 50% of the mass flow rate of the fat. Actual mass flow ratescan be determined by the volume of the reactor such that residence timeof the fat is on the order of 2 to 3 hours.

When hydrolysis proceeds in a continuous process (e.g., countercurrentflow), it is beneficial for the reactor to include a sensor fordetecting the interface level between the oil and the water/glycerinvolumes. For example, the sensor can be an electrical impedance probepositioned at the interface and useful for sensing a change in impedanceif the interface level moves so that the probe is in water rather thanoil/fat (and vice versa). If the interface level rises so that the probeis in the water, impedance will tend to drop to a much lower value, andthis provides a control signal that the system needs to allow more ofthe water/glycerin mixture to exit the reactor while holding FFAs. Thiscan be achieved, in certain embodiments, by having two pressure reliefvalves: one for FFAs and one for the water/glycerin mixture. Thesepressure relief valves can be provided in series with on/off valvescontrolled by the interface signal sensor in such a way as to maintainthe desired interface level in the reactor during continuous influx(pumping) of the oil/fat and water reactants. This allows formaintaining direct control of the mass flow ratios without requiringprecise, direct control of mass flow rates over long time periods.

The fat rises through the hot glycerol-water collecting section at thebottom of the column and passes through the oil-water interface into thecontinuous phase, the oil layer in which hydrolysis takes place. Directinjection of high-pressure steam quickly heats the reaction mixture tothe desired temperature. In certain embodiments, hydrolysis is carriedout at a temperature of about 220° C. to about 300° C. In furtherembodiments, hydrolysis is carried out at a temperature of about 230° C.to about 290° C., about 240° C. to about 280° C., or about 250° C. toabout 270° C. In one embodiment, the temperature is raised to about 260°C.

Heating of the hydrolysis reactor can be by any useful method. Incertain embodiments, heating can be via electromagnetic induction of thereactor vessel. In such embodiments, preheated water can be injectednear the reaction temperature into the vessel. In a specific embodiment,it is possible to preheat the water to a saturation pressure slightlyabove the hydrolysis vessel operating pressure, which can induce steamproduction upon entry into the reaction vessel. In specific embodiments,the supply of reaction products entering the reaction vessel is alsoheated to avoid artificially lowering the process temperature of thehydrolysis reactor. For example, the supply lines for the reactants(particularly sections of the lines that are immediately prior to entryinto the hydrolysis reactor) can be coiled around the exterior of thehydrolysis reactor but within the reactor insulation blanket.

Preferably, the pressure of the reactor column is great enough to keepthe water in the reactor from flashing to steam. Thus, at any giventemperature during the hydrolysis is carried out, the minimum pressuretracks the P-T line for water between the triple point and the criticalpoint. At any given temperature, the pressure can be greater than thisminimum so long as the pressure does not exceed reactor limitations.Therefore, the reactor pressure during hydrolysis is preferablymaintained at a pressure greater than the steam pressure so as tomaintain the water in a liquid phase. For example, when the reactortemperature is about 260° C., the pressure required to maintain thewater in a liquid state is approximately 700 PSIA (4.8 MPa). Thus, incertain embodiments, the reactor pressure during hydrolysis ismaintained in the range of about 0.5 MPa to about 20 MPa, about 1 MPa toabout 15 MPa, about 2 MPa to about 10 MPa, or about 4 MPa to about 8MPa.

The process of the invention splits fats in 98-99% efficiency withlittle or no discoloration of the fatty acids and an efficient use ofsteam. Fatty acids coming from the top of the reaction tower can beinjected directly into stage two after pressure/temperature adjustmentsto match the requirements of the deoxygenation process. A mixture ofwater and glycerol can be removed from the bottom of the reactor. Whileother processes the may produce glycerol as a by-product simply removeit as an unwanted impurity, the process of the present inventionutilizes the produced glycerol as an important reaction product thatserves to greatly improve the overall efficiency of the process. Theimportance of the produced glycerol is further described below.

In preferred embodiments, fats and water supplies aredegassed/de-aerated before injection into the splitting tower. Oxygenremoval is particularly desirable to prevent unwanted side-reactionsduring the inventive process. De-aeration can be carried out accordingto any appropriate method. For example, de-aeration can be achieved byapplication of a vacuum for a period of time sufficient to remove oxygenfrom the reactants. De-aeration can further include circulating theliquid to be de-aerated so as to expose all layers of the liquid andenable entrapped gasses to overcome the surface tension and escape theliquid. In specific embodiments, such as when the lipidic biomasscomprises highly saturated materials, such as beef tallow, de-aerationis preferably performed after pre-heating the material to maintain aliquid state. De-aeration is preferably carried out upstream from thehydrolysis injection pumps.

The ability to convert lipidic biomass to free fatty acids through aninitial hydrolysis step is illustrated in FIG. 3. In one embodiment,virgin canola oil was converted to FFAs by heating the oil in thepresence of water to a temperature of about 260° C. at a pressure ofabout 5 MPa. The FFA conversion rate was 100%, with the significantconversion products being oleic acid (C₁₈) and palmitic acid (C₁₆).

Catalytic Deoxygenation of FFAs

Following the conversion of the lipidic biomass to free fatty acids, theFFAs are converted to straight-chain paraffins (i.e., n-alkanes) via areduction process. This step can be carried out in the gas phase (e.g.,using a fixed bed catalyst) or in the liquid phase (e.g., using astirred autoclave reactor with a catalyst slurry/dispersion).

Although reduction processes have been previously performed, the presentinvention recognizes that catalytic reduction processes are needed toprovide reliable, consistent deoxygenation of the FFAs produced in stepone of the inventive process to provide a constant stream of n-alkanesfor the final step of the inventive process. Accordingly, the reductionprocess according to the invention generally comprises contacting FFAswith an appropriate catalyst. In one embodiment, the FFAs can be passedthrough a fixed-bed catalyst, such as palladium on carbon (Pd/C). Inanother embodiment, the FFAs can be combined with a slurry of Pd/C in astirred autoclave using solvent.

Deoxygenation is generally understood as relating to a chemical reactionresulting in the removal of oxygen. In the present invention,deoxygenation of FFAs is a reversible reaction that can proceed ineither of two mechanisms, which are shown below in Formula (8), whereinR is a hydrocarbon chain.

While decarboxylation and decarbonylation will both proceed over a Pd/Ccatalyst, decarboxylation is the primary reaction pathway, and the rateof decarboxylation is generally at least an order of magnitude fasterthan that of decarbonylation. When the n-alkane reaction product fromthe deoxygenation reaction is used as the reaction solvent (which ismore fully described below) and the deoxygenation reaction is performedunder hydrogen, the decarbonylation pathway is more significant, sinceit is not slowed due to microscopic reversibility. It is notable,however, that stearic acid decarboxylation is much slower in heptadecanesolvent with a 10% H₂ atm. The reaction is driven toward the reactionproduct by constant 10% H₂ sparge, which purges the formed CO₂ from thereactor. This is illustrated in Formula (9) and is also more fullydescribed below. The decarboxylation rate is slowed in heptadecane dueto equilibrium limitations as seen in this scheme. The decarbonylationpathway is unaffected by the change in solvent since both CO andheptadecane are kept at low concentrations keeping the reversedecarbonylation reactions to a minimum.

According to the present invention, this “step 2” reaction pathway cangenerically be referred to as a reduction reaction or a deoxygenationreaction. Both terms are meant to encompass both the decarboxylationreaction and the decarbonylation reaction. Since decarboxylation is theprimary reaction pathway, particularly when using preferred catalysts,the discussion relating to conversion of FFAs to n-alkanes may beparticularly described in terms of the decarboxylation reaction.However, the invention is not to be considered as being limited todecarboxylation. Rather, a decarbonylation mechanism is fullyencompassed by the invention, particularly in embodiments where n-alkaneproduct is recycled as the reaction solvent.

Although decarboxylation can be achieved through application of highheat in the presence of a high boiling solvent, such thermaldecarboxylation is ineffective for complete and consistent reaction ofFFAs into their corresponding n-alkanes. In comparison, however,catalytic decarboxylation according to the present invention providesfor very good selectivity and a conversion rate approaching 100%. Inspecific embodiments, the catalytic decarboxylation has a conversionrate to the corresponding n-alkane of at least about 70%, at least about75%, at least about 80%, at least about 85%, at least about 90%, atleast about 92%, at least about 95%, at least about 96%, at least about97%, at least about 98%, or at least about 99%.

The ability to achieve complete conversion is particularly illustratedin FIG. 5, which shows the results of one evaluation of catalyzed versusuncatalyzed decarboxylation. Specifically, stearic acid wasdecarboxylated into heptadecane in a 50 mL continuously stirredautoclave reactor using dodecane as a solvent under either catalytic ornon-catalytic conditions. In both tests, the stearic acid was heated to300° C. at 1.5 MPa pressure for varying residence times. In the firsttest, no catalyst was used. In the second test, a 5% Pd/C catalyst wasused.

As shown in FIG. 5, the upper graph shows a small rate of conversion ofstearic acid to heptadecane with a large residual amount of stearic acidremaining. In particular, the graph of the uncatalyzed decarboxylationis show at 100× magnification so that the conversion graph is visuallymeaningful (i.e., showing an abundance of heptadecane of approximately40,000). In contrast, the lower graph shows a nearly 100% conversion ofstearic acid to heptadecane. Note that the graph of catalyzeddecarboxylation is shown at 1× magnification, and the abundance ofheptadecane in the catalyzed reaction is in excess of 4,000,000 (i.e.,more than 100 times greater conversion than in the uncatalyzedreaction). Thus, FIG. 5 clearly illustrates the superior resultsobtained using catalytic decarboxylation as opposed to thermaldecarboxylation alone.

Decarboxylation of carboxylic acids was first reported by Maier, et al.(Chemische Berichte 115: 225-229, 1982) using gas-solid (heterogeneous)catalysis over supported palladium and nickel catalysts in the presenceof hydrogen. For straight-chain carboxylic acids, palladium waspreferred over nickel. The longest straight-chain acid investigated byMaier et al. was octanoic acid (C₈). According to the present invention,however, it is possible to successfully decarboxylate a longer chaincarboxylic acid (e.g., C₁₈ compounds, such as stearic acid, or evenhigher carbon compounds) in the gas phase. Such gas phasedecarboxylation generally comprises vaporization of the lipidicfeedstock. For example, in one embodiment when using a feedstockcomprising stearic acid, it is necessary to heat to a temperature of atleast about 361° C. (the boiling point of stearic acid).

Gas phase catalytic deoxygenation can be carried out by injecting theFFAs from the hydrolysis step into a suitable reactor vessel in fluidcommunication with a catalyst chamber and heating to a temperaturesuitable to vaporize the FFAs. The vaporized FFAs move through thecatalyst chamber where conversion to the corresponding n-alkane on theorder of 100% is achieved. The product can then proceed through acooling zone for condensation of the n-alkanes. In certain embodiments,it can be useful to purge the system with H₂ to remove oxygen prior toheating to the FFA vaporization temperature.

The results of gas phase decarboxylation of stearic acid according toone embodiment of the present invention are illustrated in FIG. 6through FIG. 8. Specifically, stearic acid was heated to a temperatureof at least 361° C. in the presence of a 5% Pd/C catalyst to achieve gasphase decarboxylation. As shown in FIG. 6, the desired product,n-heptadecane, was formed as the major reaction product. The smallamounts of hexadecane and pentadecane formed are believed to arise fromimpurities present in the starting material, which further illustratesthe ability to effectively form n-alkanes in the decarboxylation step ofthe invention.

In another embodiment, stearic acid was again heated to a temperature ofat least 361° C. in the presence of a 5% Pd/C catalyst to achieve gasphase decarboxylation. As shown in FIG. 7, the desired product,n-heptadecane, was again formed. Gas phase decarboxylation in this casewas also shown to effect cracking, cyclization, and aromatization. Thehighest peak in FIG. 7 (shown at time 24.05) belongs to a group ofbenzene derivatives, and the corresponding mass-spectrometer (MS) plotof this peak is provided in FIG. 8. The small peak at 77 indicates thebenzene ion, the molecular weight of benzene being about 78 da. Theability to effect these further reactions can be particularly beneficialdepending upon the type of fuel desired for production. For example,since jet fuel typically contains roughly 20% aromatic components, suchreaction could be useful to forming a product stream that isspecifically designed for jet fuel production. This could reduce theamount of further reactions needed in the reforming step of the presentinvention to arrive at the desired fuel product. In addition to stearicacid, gas phase decarboxylation according to the present invention hasbeen shown to be effective in other C₁₈ acids, such as oleic acid andlinoleic acid.

Liquid phase deoxygenation is also effective according to the presentinvention. For example, FIG. 9 is a GC/MS chromatogram of the reactionproduct of decarboxylation of stearic acid carried out using a 50 mLstirred autoclave reactor. The stearic acid in a dodecane solvent washeated to about 300° C. while contacted with a 5% Pd/C catalyst. As seenin FIG. 9, heptadecane is formed as the major reaction product. As alsoseen in FIG. 9, the dodecane solvent is also present in the reactionproduct. Thus, when such a typical solvent is used, it is necessary toisolate the reaction product from the solvent prior to introducing thereaction product into step three of the inventive process.

Snåre, et al. (Industrial Engineering Chemistry Research 45(16):5708-5715, 2006) investigated the deoxygenation of stearic acid as analternative process for biodiesel production from FFAs using aliquid-phase batch process with dodecane as the solvent (requiring asolvent-to-FFA mass ratio of 19:1). As pointed out above, a separationprocess was required to recover the products and remove the solvent.According to the present invention, however, it is possible to carry outliquid phase decarboxylation of stearic acid in heptadecane, which isthe decarboxylation product of stearic acid. Thus, in certainembodiments, the present invention provides for liquid phase catalyticdecarboxylation of a long chain FFA into its corresponding n-alkanewhile recycling a portion of the reaction product as the solvent.Employing the product of the reaction as the solvent greatly increasesthe thermodynamic efficiency because the need to heat a separate solventstream is eliminated. This is further advantageous because it eliminatesthe need for an additional separation process because the product andthe solvent are the same. Thus, the continuous nature of the inventiveprocess is conserved by recycling a portion of the decarboxylationreaction stream as the decarboxylation solvent in a liquid phasereaction.

As previously noted, deoxygenation is a reversible process, and therecan thus be equilibrium limitations on the decarboxylation and/ordecarbonylation reactions taking place. For example, when using recycledn-alkane reaction product as reaction solvent, deoxygenation can beslowed in both the decarboxylation and decarbonylation pathways.Accordingly, in certain embodiments, it is beneficial to including apurging step to facilitate reaction. For example, removal of CO₂ (adecarboxylation product) can be useful to drive equilibrium towardreactants, as illustrated in Formula (8).

Since decarboxylation is the dominant deoxygenation pathway over a Pd/Ccatalyst, hydrogen generally is not required for the reaction.Nevertheless, in specific embodiments, it can be particularly useful tointroduce hydrogen into the reaction. Table 4 below provides the resultsof one evaluation of the liquid phase decarboxylation of saturated andunsaturated C₁₈ FFAs using a Pd/C catalyst in the presence and absenceof H₂. As seen in Table 4, the decarboxylation of unsaturated FFAs, suchas oleic acid, only proceeds to a significant extent in the presence ofH₂. In this evaluation, decarboxylation was carried out at a temperatureof 300° C. and a pressure of 15 atm using 1.6 g of each reactant and 350mg of Pd/C catalyst. The first five tests were carried out using 23 g ofdodecane solvent. The final test with stearic acid was carried out using23.6 g of heptadecane as solvent. Thus, the present invention is furtherbeneficial in that the decarboxylation reaction parameters can beoptimized, such as inclusion or exclusion of H₂, depending upon thefeedstock composition and the desired end product. Moreover, thebeneficial aspect of using recycled decarboxylation product as thedecarboxylation solvent (Test 6 in Table 4) does not adversely affectthe conversion of the FFA to its corresponding n-alkane. Moreover, thepresent invention is further beneficial, as illustrated in FIG. 2, inthat at least a portion of the H₂ used in this decarboxylation step canbe provided as a recycled waste stream from the reforming step describedin detail below.

TABLE 4 Reactant Heptadecane Other C₁₇ Test FFA Reaction Conver- YieldYield Number Reactant Atmosphere sion (%) (wt. %) (wt. %) 1 Stearic He92 76 16 2 Stearic 10% H₂ 100 100 0 3 Oleic He 12 1 7 4 Oleic 10% H₂ 100100 0 5 Linoleic 10% H₂ 100 100 0 6 Stearic 10% H₂ 100 100 0

The deoxygenation kinetics of stearic acid and oleic acids in H₂ areclosely similar, as shown in FIG. 10, with complete FFA conversionoccurring in approximately 30 minutes and providing essentially 100%yield of n-heptadecane. Specifically shown in FIG. 10 is the results ofstearic and oleic acid decarboxylation reactions in 10% H₂ and dodecanesolvent at 300° C. over 5% Pd/C catalyst for different reaction times.Shown are oleic acid conversion (Δ), oleic acid heptadecane yield (□),stearic acid heptadecane yield (∘), and oleic acid result with ½catalyst (⋄).

The results shown in FIG. 10 indicate that oleic acid is hydrogenatedfirst to stearic acid before decarboxylation to n-heptadecane. This isshown below in Formula (10).

Other known processes that purport to form fuels rely heavily on the useof H₂ as a reactant, particularly in hydrotreating processes, to achieveoxygen removal. The present invention, however, is not so limited.Rather, as pointed out above, deoxygenation according to the presentprocess is catalytically achieved, and amount of H₂ used is generally afunction of the lipidic biomass feedstock. For example, when usinghighly saturated materials, H₂ can be relegated to a basicallynon-reactive status, being used mainly as a purge material, such asdescribed above in relation to gas-phase catalytic deoxygenation. Whenusing a less saturated (i.e., more olefinic) feedstock, additional H₂can be used to encourage production of n-alkanes.

While Pd/C is preferred as an efficient FFA decarboxylation catalyst,the use of other catalysts is not excluded in the invention. Rather, anycatalyst effective in facilitating FFA decarboxylation can be used as acatalyst in the present invention. In particular, any noble metal may beused, particularly platinum and palladium. Moreover, bimetalliccatalysts may also be used according to the invention and may have theformula M_(N)-X, wherein M_(N) is a noble metal and X is a complementarymetal, which can include other noble metals or transition metals.Moreover, supports other than carbon can be used according to theinvention. Non-limiting examples of supports useful according to theinvention in addition to carbon include silicates, as well as any othersupport-type material which, preferably, is non-acidic and substantiallyor completely inert (i.e., have little or no inherent catalyticfunction). Non-limiting examples of further catalysts that could be usedaccording to the invention include Ni, Ni/Mo, Ru, Pd, Pt, Ir, Os, and Rhmetal catalysts.

The present invention is particularly distinguishable from known methodsthat rely on thermal decarboxylation, which require temperatures inexcess of 400° C. to achieve appreciable decarboxylation. Even greatertemperatures (e.g., in excess of 500° C.) can be required to achieveuseful levels of decarboxylation. The present invention, however,benefits from the catalytic nature of the deoxygenation. Particularly,it is possible to proceed with significantly lower reaction temperatureswhile still achieving excellent deoxygenation (such as shown above inreference to FIG. 5). In certain embodiments, to carry out catalyticdeoxygenation in a liquid phase reaction, the FFAs from the step onehydrolysis are heated to a temperature of up to about 325° C. In otherembodiments, the FFAs are heated, in the presence of a suitablecatalyst, to a temperature in the range of about 200° C. to about 320°C., about 250° C. to about 320° C., about 270° C. to about 320° C., orabout 290° C. to about 310° C. Reaction pressure can be in the range ofabout 400 kPa to about 800 kPa, preferably about 500 kPa to about 700kPa.

As particularly illustrated in relation to FIG. 5, catalyticdecarboxylation occurs at 300° C. in the liquid-phase under conditionswhere there is no thermal reaction in the absence of a catalyst.Moreover, reaction selectivity for n-alkanes is very high in thecatalytic process of the present invention. For example, in certainembodiments, catalytic deoxygenation occurs in a manner such thatgreater than 90% of the hydrocarbon reaction products are n-alkanes. Infurther embodiments, deoxygenation occurs in a manner such that greaterthan 92%, greater than 95%, greater than 97%, or greater than 98% of thehydrocarbon reaction products are n-alkanes. Such selectivity is notseen in thermal decarboxylation reactions.

In certain embodiments, catalytic deoxygenation can be described asbeing carried out at a temperature at which deoxygenation does notsubstantially proceed by thermal action alone. In other words, thecatalytic reaction conditions are such that, in the absence of thecatalyst, the process would result in less than 50% by weight conversionof the FFAs to their n-alkane reaction product.

The largest single energy cost in the process of the invention is thecost of heating the solvent to reaction temperature. Accordingly, inpreferred embodiments, the inventive process can be optimized tominimize or eliminate the use of an added solvent in the reactionprocess. In one particular embodiment, the reaction can proceed inliquid n-alkane (without additional solvent) that is recycled from thereaction process. In such an embodiment, the catalyst can be used in aslurry/dispersion with the FFAs. Moreover, since the decarboxylation isproceeding catalytically and is not dependent upon temperature alone,less heat is required to maintain the lower process heat used in thecatalytic decarboxylation process.

The benefits of catalytic decarboxylation according to the presentinvention are particularly seen in the liquid phase reaction usingrecycled n-alkane as the reaction solvent. As pointed out above,traditional thermal decarboxylation is typically carried out in theliquid phase using a hydrocarbon solvent, such as dodecane. Such areaction scheme would not typically be generally regarded as beingcombined with a catalytic deoxygenation process. For example, is askilled person simply sought to introduce a catalyst into a thermaldecarboxylation set-up, the overall process would be hindered by theadded requirement to separate the n-alkane product from the solvent, aswell as the catalyst. In the present invention, however, thesedifficulties are overcome. For example, in certain embodiments, it ispossible to use a catalyst slurry/dispersion with a solvent that isrecycled n-alkane decarboxylation reaction product.

In further embodiments, the reaction can be carried out in a continuousstirred autoclave with recycling of reaction components. Further, gasphase fixed bed reactors, as well as liquid phase slurry reactors couldbe use. Of course, these are merely representative types of reactors andare not intended to limit the scope of the invention. One example of amethod for heterogeneous catalytic deoxygenation is disclosed by Snareet al., I. &E. Chem. Res. 45(16) 5708-5715 (2006), which is incorporatedherein by reference in its entirety.

Reforming of Long Chain Alkanes

After formation of the n-alkanes, as described above, the resultingcompounds can be reformed into compounds typical of the type of fuelbeing prepared. For example, gasoline is generally a mixture of C₅-C₁₂compounds, and kerosene is typically a mixture of C₁₂-C₁₅ compounds. Jetfuels, which are kerosene-based, can be prepared through reforming ofn-alkanes to provide a mixture of compounds having pre-defined carbonchain lengths, chain conformations, and compound ratios (e.g., themixture described in Table 1). Similarly, diesel and gasoline are bothmixtures of hydrocarbon compounds in the desired chain length, chainconformation, and compound ratios. Knowing these desired compositions,it is possible to set up the reforming reaction(s) to form the compoundshaving the necessary chain lengths, the necessary conformations, and thenecessary compound ratios to be considered the desired fuel type (i.e.,either a jet engine fuel, a diesel engine fuel, or a gasoline enginefuel).

For example, as previously noted, jet fuels typically comprisen-alkanes, iso-alkanes, cyclics, and aromatics in specific ratios.Gasoline engine fuels similarly comprise varying ratios of aromatics,n-alkanes, iso-alkanes, cyclics, and alkenes. Diesel engine fuelstypically have a less complex structure exhibiting a higher averagemolecular weight and a lower aromatic content. Standards for fuelcompositions are well known, and it is particularly possible accordingto the present invention to prepare a particular fuel to meet a specifictarget composition, which can be based upon known fuel compositionstandards.

Reforming according to the invention can generally encompass one or morereactions that alter n-alkanes through changing the carbon chain lengthof the n-alkanes, changing the structure of the n-alkanes (e.g.,converting from a straight chain to a branched chain or a ringstructure), or altering the intramolecular bonding of the n-alkanes(e.g., converting single bonds to double bonds). For example,hydrocracking can be used to alter the chain length of alkanes, andhydroisomerization can be used to change the structure of the alkanes,such as to form a specified content of cycloalkanes and isoalkanes inthe prepared fuel. Similarly, aromatization can be used to alter theintramolecular bonding of the alkanes to produce a specified content ofaromatic compounds in the prepared fuel. In certain embodiments,reforming comprises two or more separate catalytic processes, eachperformed using different reaction parameters (such as catalyst type,temperature, pressure, or reactants). The output of the separatereforming steps can then be blended together to achieve the requisiteblend of compounds to form the desired fuel composition.

For example, in one embodiment, the n-alkane stream from thedeoxygenation step described above is split upon entering the reformingstage. Part of the stream may be directed to two or more separatereactors set up to carry out one or more of hydroisomerization,hydrocracking, aromatization, and cyclization. In such an embodiment,each reactor would set up under the required reaction parameters (e.g.,catalysts, reactor temperature, and reactor pressure) needed to carryout the desired reaction. Each reforming reactor would reform then-alkane stream into the desired compound(s), and the reaction productcould be withdrawn from the reactor. The reaction streams from eachreforming reactor could be then combined so that a final fuel product isformed having the necessary compounds in the necessary ratios to beconsidered a specific fuel type (e.g., jet engine fuel, diesel enginefuel, or gasoline engine fuel).

For example, in one embodiment (such as in the preparation of a jet fuelof a gasoline engine fuel), approximately 10-15% of the n-alkane streamcould be diverted into a high temperature reactor set-up for formingaromatics, and the remaining portion of the n-alkane stream could bedirected into an HI/HC reactor to form the necessary compounds of therequired chain length (e.g., in the C₅-C₁₂ range for gasoline) and thecorrect conformation (e.g., cycloalkanes and olefinics). The HI/HCreaction parameters, as discussed herein, could be varied based on thedesired fuel composition to provide the correct ratio of alkanes,cycloalkanes, and alkenes.

In other embodiments, though, it is possible to prepare the final fuelcomposition using only a single reforming reactor. For example, infuels, such a diesel engine fuel, where aromatics are not necessarilyrequired, all necessary reforming could be carried out in a single HI/HCreactor using suitable reaction parameters, as described herein.

In still further embodiments, it is useful to use two or more reformingreactors in series to achieve the desired final fuel composition. Forexample, in one embodiment, the n-alkanes from the deoxygenation stepcan proceed to a catalytic reactor for carrying HI/HC reactions. Atleast a portion of the HI/HC products can then proceed directly into asecond catalytic reactor to produce aromatic and cycloalkanes. Such areactor series set-up can be particularly useful in processes accordingto the invention for preparing a biogasoline product.

As illustrated by the foregoing, the present invention is particularlycharacterized by its broad applicability for preparing a number of fuelproducts. Thus, the present invention is especially beneficial becauseof its customizability, which arises from the recognition of a series ofprocesses that, when carried out in series, allow the user to identify adesired fuel product and then adjust the reaction parameters asnecessary to achieve production of that desired fuel. For example, asdescribed herein the process reaction parameters can be adjusted tofavor reforming of n-alkanes into hydrocarbon compounds typical of adesired fuel. The ease of forming compounds in carbon chain length,chain conformations, and compound ratios necessary to equate to aspecific fuel type can, in part, depend upon the chain length of then-alkanes entering the reforming process. Thus, to prepare a specificfuel type, it may be desirable for the n-alkanes entering the reformingprocess to be predominantly of a specific chain length (e.g.,predominately C₁₅-C₁₇ n-alkanes). According to the present invention, itis possible to customize the deoxygenation step so that the n-alkanesproduced thereby are predominately in the desired chain length range.This customization of the deoxygenation step can be facilitated bycarrying out deoxygenation on FFAs that already have hydrocarbon chainsin the desired length (e.g., use of a C₁₈ FFA, such as stearic acid, toprepare a C₁₇ n-alkane, such as heptadecane). The desired FFAs can beprovided by beginning the process with a lipidic biomass that is rich inthe desired FFAs (e.g., triglycerides having fatty acid tails of theappropriate chain length). Thus, it is clear that the entire process ofthe present invention can be customized to prepare a specific fuel. Forexample, if biogasoline is desired, the lipidic biomass can be chosen tobe a material rich in triglycerides that will undergo hydrolysis toproduce FFAs that will undergo deoxygenation to produce n-alkanes thatcan be reformed into a combination of compounds of the correct carbonchain length, chain conformation, and compound ratio necessary to meetthe standards to be considered a gasoline engine fuel. The sameconsiderations can be made to prepare a fuel that meets the requisitestandards for a jet engine fuel or a diesel engine fuel.

In certain embodiments, the process of the invention can be described asincluding a step of recovering hydrocarbon compounds. Said step ofrecovering is intended to encompass any of the various methods describedherein for achieving the correct combination of compounds to make up thedesired fuel product. For example, in one embodiment, reforming cancomprise using separate reactors to form isoalkanes, aromatics, andcycloalkanes, and the recovering step can comprise obtaining theisoalkanes, aromatics, and cycloalkanes from each, separate reactor,optionally including n-alkanes, and combining all reforming productstreams in the correct n-alkanes:isoalkanes:aromatics:cycloalkanes ratioto be the desired fuel. In other embodiments, however, such as whenreforming is carried out using reactors in a series or where reformingcomprises the use of a single reactor, the recovering step can simplycomprise collecting a single stream of hydrocarbon compounds that isalready in the correct n-alkanes:isoalkanes:aromatics:cycloalkanes ratioto be the desired fuel. Thus, in separate embodiments, recovering canrequire a specific step of mixing individual product streams or cansimply require recovering a stream that is already in the end-productform.

In various embodiments of the invention, reforming includes the use ofcatalysts that are chosen based on the desired end product. Forhydrotreating, supported Pt is preferred, and Pt-X bimetallics (X═Ir,Re, Sn) supported on an acidic (Cl-modified) alumina are preferred fordehydrocyclization (aromatization). The desired extent of HI/HC of then-alkane mixture from the deoxygenation step of the invention processcan depend on the biofuel target (biodiesel, biogasoline, or bio-jetfuel). For a biodiesel, a small degree of HI (i.e., formation ofbranched compounds) can be desirable for improving the cold-flowproperties of the fuel. Extensive branching, though is undesirable sincethis will reduce the Cetane Index. For a bio jet fuel, moderate HI/HC ofthe normal C₁₅-C₁₇ alkane feed can be useful to reduce the averagecarbon number and improve the cold-flow properties of the fuel. For abiogasoline, extensive hydrocracking of multi-branched alkanes can beuseful to obtain the desired C₄-C₈ branched alkanes with high octanenumbers. Over-cracking, though, to light (<C₄) alkanes is preferablyavoided.

A delicate balance between metal and acid functions determines theperformance of hydrotreating catalysts. In the present invention,catalysts prepared from amorphous oxides (e.g., silica-alumina),crystalline aluminosilicates (e.g., zeolites), andsilicoalumino-phosphates (e.g., SAPO 11) with a range of Pt metalloadings can be used.

Hydroisomerization/hydrocracking (HI/HC) of the n-alkanes generallycomprises contacting the n-alkanes prepared in the reduction step with acatalyst under conditions appropriate to form the desired compounds inthe desired ratios, and the reforming process can particularly becarried out using a monofunctional or bifunctional solid catalyst.Reforming is particularly useful in that the process can be directedtoward preparation of specific compounds depending upon the desired endproduct fuel. In particular, the process can be tuned to provide thedesired mix of isoalkanes, cycloalkanes, and aromatics typically presentin a specific fuel type. Generally, this can be achieved throughcontrolling the following process parameters: catalyst compositionstructure, reaction temperature, reaction pressure, reactor residencetime, and ratio of hydrogen to n-alkanes. For example, highertemperatures and decreased hydrogen pressure both favor aromatization.Parameter control and the effects thereof are more fully detailed below.Generally hydrocracking is favored using more acidic catalysts andlonger residence times. Typical reaction conditions can comprise atemperature of about 350° C. to about 380° C. and a pressure of about 1MPa to about 10 MPa.

The reforming step of the reaction can be used to prepare compounds of avariety of chain lengths, generally depending upon the desired endproduct and the content of the starting material (the lipidic biomass).As previously noted, animal fats generally comprise a majority of C₁₆and C₁₈ fatty acids. Thus, a majority of the n-alkanes resulting fromthe reduction step described above have similar carbon chain lengths. Ofcourse, the content of the lipidic biomass can be customized to resultin the production of n-alkanes that are particularly amenable toreforming into fuels having specific compositions. Generally, then-alkanes mixture introduced into the reforming step of the inventioncan comprise C₆-C₂₀ hydrocarbons. In specific embodiments, the n-alkanesmixture introduced into the reforming step of the invention can compriseC₁₅-C₁₇ hydrocarbons.

In one embodiment, the reforming is particularly customized forformation of jet fuel. In such an embodiment, the reforming can becustomized to prepare a jet fuel mixture comprising primarily of C₉-C₁₈hydrocarbons. Preferably, the mixture comprises C₁₀-C₁₄ hydrocarbons,and particularly C₁₀-C₁₄ isoalkanes. In further embodiments, thereforming step can be customized to favor formation of carbon chainlengths such that specified compound ratios can be achieved. Catalystcomposition and reactor conditions can be adjusted to favorhydrocracking products (lower molecular weight compounds) orhydroisomerization products (more highly branched isomers), particularlyC₁₀-C₁₄ isoalkanes.

In another embodiment, the reforming is particularly customized forformation of gasoline. In such an embodiment, the reforming can becustomized to prepare a mixture of compounds comprising primarily C₇-C₁₁hydrocarbons. Preferably, the mixture is optimized to comprise amajority of C₈ hydrocarbons, and particularly C₈ isoalkanes.

A variety of catalysts can be used according to the present inventionincluding monofunctional and bifunctional catalysts. Monofunctionalcatalysts preferentially comprise a noble metal and can includebimetallics having the formula M_(N)-X, wherein M_(N) is a noble metaland X is a complementary metal, including other noble metals. Inpreferred embodiments, the catalyst comprises platinum. Bifunctionalcatalyst comprise a metal functional component and a non-metalfunctional component. The metal functional component of a bifunctionalcatalyst according to the present invention can comprise a noble metal(or bimetallic) as described above in relation to monofunctionalcatalysts. The non-metal functional component of a bifunctional catalystaccording to the invention preferably comprises a solid acidic material,such as an acidic metal oxide. In certain embodiments, the acidfunctional portion of the bifunctional catalyst can be selected fromamorphous oxides (e.g., silica-alumina), aluminosilicate zeolites (e.g.,γ and β), and silicoalumino-phosphates (e.g., SAPO 11). Of course, theforegoing materials are only provided as examples and are not intendedto limit the scope of the invention. Rather, other solid materialsproviding acidic reaction sites and being capable of performingcatalytic functions as described herein could be used according to theinvention.

In addition to the chemical makeup, catalysts according to the inventioncan also vary based on physical structure. For example, a bifunctionalcatalyst according to the invention can be provided as discrete metalfunctional particles and separate discrete acidic functional particles.In a preferred embodiment, the acidic functional component forms asubstrate for the metal functional component (e.g., Pt supported onsilica/alumina). Moreover, a monofunctional catalyst according to theinvention can comprise discrete particles of a metal functionalcomponent alone or supported on a non-functional substrate.

Reforming reactions are typically carried out at increased temperatureand pressure. In certain embodiments, HI/HC reforming of n-alkanes canbe carried out at a temperature of up to about 600° C., up to about 550°C., or up to about 525° C. In specific embodiments, reforming reactionsare performed in a temperature range of about 300° C. to about 600° C.,about 325° C. to about 550° C., about 350° C. to about 500° C., about350° C. to about 450° C., or about 400° C. to about 450° C. Reactorvessel pressure during reforming is typically in the range of about 0.5MPa to about 20 MPa, about 1 MPa to about 15 MPa, or about 1 MPa toabout 10 MPa. Preferably, the reactions are carried out in a hydrogenatmosphere. In reactions such as dehydrocyclization, optimum hydrogenpressure can be varied as necessary to suppress coke accumulation(mainly from polycyclic aromatic hydrocarbons) leading to catalystdeactivation.

The selectivity of hydroisomerization/hydrocracking can be controlledaccording to the invention through controlling the balance between themetal and acid functions of the bifunctional HI/HC catalyst. Inparticular, the content of the metal functional portion of thebifunctional catalyst can vary over a range of metal loadings. Forexample, in a bifunctional catalyst, the metal functional component cancomprise up to about 50% by weight of the catalyst, up to about 40%, upto about 30%, up to about 20%, up to about 10%, or up to about 5% byweight of the catalyst. In specific embodiments, the metal functionalcomponent comprises about 0.01% to about 10% by weight of the catalyst,about 0.02% to about 9% by weight, about 0.05% to about 8% by weight,about 0.1% to about 7% by weight, about 0.1% to about 6% by weight, orabout 0.1% to about 5% by weight of the catalyst.

The reforming effect can also be controlled by altering the reactiontemperature and pressure within the previously described ranges. Forexample, higher reaction temperatures (in the range of 400-450° C.) andlower hydrogen pressures will generally favor dehydrocyclization ofalkanes to form aromatics. Further, higher temperatures and higherconversions will generally favor hydrocracking over hydroisomerization.

Petroleum-derived fuels (especially jet fuel and gasoline) containcycloalkanes and aromatic compounds. Consequently, to ensure completecompatibility of second generation biofuels with existing engines, itmay be necessary to produce cycloalkanes and aromatics frombio-renewable fats and oils. Accordingly, reforming reaction parameterscan further be controlled to favor vapor-phase dehydrocyclization (DHC)of alkanes to aromatics. Aromatization and cyclization of n-alkanes canbe achieved, according to certain embodiments of the invention, usingsupported metal catalysts (preferably Pt-containing catalysts). Hightemperatures (such as about 400-450° C.) are useful fordehydrocyclization (DHC) of alkanes to aromatics, since the reaction isstrongly endothermic. The DHC mechanism can involve only the transitionmetal (monofunctional catalytic pathway) or the transition metal andacid sites of the support (bifunctional catalytic pathway) depending onthe catalyst composition. For example, Pt supported on a non-acidicK-exchanged L zeolite (a monofunctional pathway) is selective forbenzene formation from n-hexane via monofunctional catalysis (1-6 ringclosure). Methylcyclopentane resulting from 1-5 ring closure also occursover Pt, and the ratio of 1-6 to 1-5 ring closure products from n-hexanecan be controlled by controlling the pore geometry for non-acidicsupports.

In further embodiments, alkane DHC can be carried out via a bifunctionalpathway through use of conventional reforming catalysts, such as Pt or aPtX bimetallic (particularly wherein X═Ir, Re, Sn) supported on anacidic alumina support (such as Cl-modified supports). For example,conventional petroleum naphtha reforming catalysts that are used toproduce high-octane unleaded gasoline catalyze alkane dehydrocyclizationvia a bifunctional pathway. As previously described, the metal catalyticsites (e.g., noble metals) provide a dehydrogenation/hydrogenationfunction, and adsorption of the resulting olefins on acid sites of thesupport generates alkyl carbenium ions. The more stable secondarycarbenium ion undergoes 1-5 ring closure to yield methylcyclopentane.Subsequent metal- and acid-catalyzed reactions lead to cyclohexane andultimately benzene. This is particularly useful according to theinvention in that it allows for the reforming of a C₁₅-C₁₇ alkanefeedstock to a surrogate JP-8 fuel. Specifically, dehydrocyclization ofhigher alkanes, such as the C₈-C₉ compounds in petroleum naptha, overbifunctional catalysts results directly in 1-6 ring closure products,such as alkyl-substituted benzenes. Tests using n-tridecane andn-hexadecane as model compounds illustrated that aromatics (such astoluene, xylenes, and methyl- and dimethylnapthalenes) can be preparedin addition to hydroisomerization products. The optimum hydrogenpressure for dehydrocyclization is determined by the need to suppresscoke (mainly polycyclic aromatic hydrocarbons) accumulation leading tocatalyst deactivation.

In one embodiment, hydroisomerization/hydrocracking of the n-alkanesproduced in the previous catalytic deoxygenation step can be achievedusing a bifunctional solid catalyst consisting of platinum supported onan acidic metal oxide. The Pt sites provide adehydrogenation/hydrogenation function, and adsorption of the resultingalkenes (olefins) on the acid sites generates secondary carbenium ions.These carbenium ion intermediates undergo skeletal isomerization to morestable tertiary carbenium ions before donating a proton (H+) toregenerate the acid site. Subsequent hydrogenation of the resultingalkene (at a Pt site) produces mono-, di-, and tri-branched alkanes.Hydrocracking is a closely related process resulting from β-scission ofthe carbenium ion intermediate. The extent of the hydrocracking can becontrolled to impart particular properties to the resulting fuelproduct. For example, a limited amount of cracking of the alkane feedcan be carried out to reduce the average carbon number as necessary toimprove the cold-flow properties of the fuel. A schematic of a typicalisomerization/hydrocracking network is shown in FIG. 11.

With the appropriate balance of Pt and acid sites, the primary reactionproducts are mono-branched alkanes. Multi-branches alkanes are secondaryproducts and hydrocracking products (a mixture of medium and lowmolecular weight species, relative to the original n-alkanes) are formedin series from the multi-branched species. Consequently, higher n-alkaneconversion will favor hydrocracking products.

In a specific embodiment, a catalyst useful in a reforming step of theinventive process comprises a 1% by weight Pt on zeolite Y (Pt/Y)prepared by ion exchange. Such a catalyst was used, in one embodiment,for the reaction of liquid n-heptadecane at 300° C. in a 50 mL stirredautoclave reactor under 500 psig H₂. The reaction products after threehours reaction time are illustrated in the chromatogram shown in FIG.12. As seen therein, the major products are C₁₇ branched alkanes(including methyl, dimethyl, and trimethyl branched isomers). Alsoobserved are C₅-C₁₄ hydrocracking products. Due to the underlyingcarbenium ion β-scission) mechanism, the yields of C₁₆ and C₁₅ speciesfrom the C₁₇ feedstock are negligible. GC and quadrupole massspectrometry of the gas-phase products revealed small quantities ofmethane, ethane, propane, and butane. Evaluations using a 1 wt % Pt onmordenite (Pt/M) catalyst demonstrated higher yields of hydrocrackingproducts under similar reactions.

In certain embodiments, it is possible according to the invention toprovide catalysts and conditions that are particularly useful forproducing biogasoline, particularly from a deoxygenation reaction streamcomprising C₁₇ n-alkanes. In one embodiment, an evaluation was carriedout using liquid n-heptadecane and a Pt catalyst in a 100 mL batchreactor at 300° C. and 1000 psig H₂. The heptadecane conversion after 30minutes was essentially 100%, and greater than 95% by mass was convertedto liquid products. Gas chromatograph-mass spectrometer (GC-MS)analysis, as shown in FIG. 13, indicated that the products were amixture of branched and linear alkanes. No aromatics or cycloalkaneswere detected. Gas-phase products consisted primarily of C₁-C₄hydrocarbons.

The carbon number distribution obtained after one hour batchhydrotreating using the same catalyst and conditions was similar to thatof a typical regular unleaded gasoline, especially given the absence ofcycloalkanes and aromatic compounds (C₆ and above). This is illustratedin FIG. 14. This figure also illustrates the progressive naturehydrocracking. A 30 minute batch time yields a higher average molecularweight and more product in the middle distillate (kerosene or jet fuel)range compared to a one hour batch time.

Energy Recovery

The process of the invention is further characterized by the multipleavailable options for optimizing efficiency by converting as much aspossible of the energy content of the lipidic biomass into useable fuel.This is achieved by methods including, but not limited to, recovery andre-use of excess steam from the hydrolysis process, combustion ofglycerol by-product of the hydrolysis process with heat exchange to allthree chemical process, and recovery of internal energy of exiting fuelproduct by heat exchange to all three chemical processes.

A useful figure of merit related to energy balance is the energyconversion efficiency, as defined below in Formula (11), where LHV isthe lower heating value.

$\begin{matrix}{\underset{Efficiency}{Energy} = \frac{L\; H\; V\mspace{14mu} {of}\mspace{14mu} {Produced}\mspace{14mu} {Fuel}}{\left( {{L\; H\; V\mspace{14mu} {of}\mspace{14mu} {Reactants}} + {{Input}\mspace{14mu} {Energy}}} \right)}} & (11)\end{matrix}$

Determining conversion efficiency must take into account multiplefactors. Table 5 below provides examples of material properties that canbe used according to one embodiment of the invention for preparing jetfuel to calculate energy efficiency of the inventive process. Of course,similar considerations would come into play in other embodiments of theinventive process, such as in the preparation of biogasoline orbiodiesel.

TABLE 5 Energy Content Specific Heat Density Material (kJ/kg) (kJ/Kg ·K) (kg/m³) Triglyceride 39,000 2.21 925 Free Fatty Acid 39,000 2.00 847Water 0 4.20 1,000 Glycerol 16,700 2.38 1,261 Hydrogen 120,911 14.500.089 n-alkanes 47,279 1.90 777 JP-8 44,000 2.00 820

A detailed process flow according to one embodiment of the inventionshowing each process step is provided in FIG. 15. Table 6 belowsummarizes the energy input and output of the process (withoutimplementation of the energy conservation methods outlined below) forthe production of 100 liters of bio-JP8 prepared according to thisembodiment of the invention.

TABLE 6 Process Energy No. Description Composition Added 1 Water 2 Pumppower Water 0.08 kW 3 Heat exchanger Water 4 Heater power Water 0.17 kW5 Inlet energy in Triglycerides 54.93 kW  feedstock 6 Pump powerTriglycerides 0.13 kW 7 Heat Exchanger Triglycerides 8 Heater powerTriglycerides 0.28 kW 9 Step 1 reactor/ Water/ 0.70 kW line make-upGlycerine heat 10 Free Fatty Acids 11 Glycerine by- Water/ productGlycerine 12 Free Fatty Acids 13 Step 1 product Free Fatty stored @Acids ambient 14 Pump power Free Fatty 0.12 kW Acids 15 Heat exchangerFree Fatty Acids 16 Heater power Free Fatty 0.29 kW Acids 17 Step 2reactor/ n-alkanes 1.10 kW line make-up heat 18 Inlet energy in He/H₂1.68 kW H₂ 19 Adiabatic He/H₂ 0.05 kW compression power 20 He/H₂ not HeH₂, CO₂ recycled 21 n-alkanes 22 Step 2 product n-alkanes stored @ambient 23 Pump power n-alkanes 0.10 kW 24 Heat n-alkanes exchanger 25Heater power n-alkanes 0.25 kW 26 Step 3 reactor/ JP-8 1.70 kW line heatleak 27 Inlet energy in He/H₂ 1.68 kW H₂ 28 Adiabatic He/H₂ 0.05 kWcompression power 29 He/H₂ not He/H₂ recycled 30 Light Lighthydrocarbons hydrocarbons not used 31 45.1 kW JP-8 contained in 100 LJP8The total energy added to the system shown in Table 6 (63.31 kW) is thedenominator in Formula (10) above. The numerator is only that energythat is contained in the 100 liters of bio-JP8 fuel produced (45.1 kW).Calculation according to Formula (10) shows an energy efficiency of71.2% without inclusion of any energy conservation steps, as describedbelow. Thus, this represents a conservative energy efficiency since allenergy calculations are based on actual hardware power consumptioncurves (pumps and compressors), heat transfer effectiveness values (heatexchangers=0.7), insulation R-values (line heaters and heat loss in thereactors), and reactor throughput material loss (glycerol in Step 1, CO₂in Step 2, and light hydrocarbons in Step 3.

In particular embodiments, the process of the invention requires a totalthermal input of approximately 2.3 MJ/kg of animal fat used as thelipidic biomass fuelstock. To minimize this heat input, the process isgenerally designed to maximize the heat recovery from the end productsin preheating the fat and water in the first stage. The hydrolysis stepcan particularly be optimized according to the invention to recoverenergy for use in the process. For example, the hot glycerol/watermixture prepared by fat hydrolysis can be separated by flash evaporationof water, to yield glycerol with sufficient purity to burn efficientlyin a combustor, and the hot water can be recycled to the hydrolysisprocess. Taking into account the energy losses due to non-idealprocesses, such approaches can restore up to about two-thirds of thethermal input energy required.

Thus, in certain embodiments, the process of the present inventioncomprises recovering at least a portion of the glycerol prepared in thehydrolysis step and recycling the glycerol as an energy source. Theenergy content of the glycerol produced in the hydrolysis step isactually sufficient to provide the necessary reactor heating for allthree steps of the inventive process, as well as provide heat toreactors to alleviate heat loss to the environment during operation.Realization of the heating energy available in the glycerol by-productcan particularly be via a proprietary method and apparatus provided bythe inventors of the present invention.

Glycerol combustion can, in one embodiment, proceed via a proprietarymethod and apparatus provided by the inventors of the present invention.For example, the glycerol combustion can be carried out in an insulatedburner with a glycerol combustion chamber. Preferably, the glycerolcombustion chamber is pre-heated, and the glycerol recovered from thehydrolysis step of the present invention is introduced directly into thepre-heated glycerol combustion chamber. Optionally, the glycerol can betreated to reduce the glycerol viscosity. The glycerol can be atomizedprior to introduction into the glycerol combustion chamber. Uponintroduction of the glycerol into the combustion changer, the atomizedglycerol is combined with air and combusted to produce heat.

Pre-heating of the glycerol combustion chamber can be carried outaccording to various methods, such as combustion of a start-up fuelsource or use of resistance heating. In one embodiment, the pre-heatingstep comprises combustion of a non-glycerol fuel source (i.e., astart-up fuel source) within the glycerol combustion chamber. This ispreferably carried out for a period of time sufficient to heat thecombustion chamber to a temperature at least equal to the auto ignitiontemperature of glycerol. After the desired temperature has beenachieved, introduction of the non-glycerol fuel source can bediscontinued and fully replaced with glycerol. The transition betweenthe start-up fuel source and the glycerol can be gradual or distinct.

In specific embodiments, the step of treating the glycerol to reduce theviscosity thereof comprises reducing the viscosity of the glycerol toless than a specified viscosity. Preferably, the glycerol viscosity isreduced to less than about 20 centistokes. In specific embodiments, thestep of treating the glycerol comprises heating the glycerol source,such as up to a temperature of at least 91° C. In another embodiment thetreating step comprises combining the glycerol with a viscosity-reducingliquid, which preferentially also is combustible (e.g., kerosene).

In yet another embodiment the step of combining the atomized glycerolwith air comprises providing an aerodynamically restricted air flow suchthat the atomized glycerol is introduced into the glycerol combustionchamber with a defined flow pattern and air mixture. In a specificembodiment, such aerodynamically restricted air flow is provided by aswirl component.

Glycerol combustion for providing heat in the present inventive processcan particularly be carried out using a specifically designed glycerolcombustion apparatus. In one embodiment, the apparatus comprises thefollowing: an insulated glycerol combustion chamber being formed toprovide radiant and convective feedback heating; a glycerol input linefor introduction of the glycerol into the glycerol combustion chamber,wherein the line includes one or more components for heating ormaintaining the glycerol within the line at a temperature of at leastabout 91° C.; an atomizer attached to the glycerol input line capable ofatomizing the glycerol prior to introduction of the glycerol into theglycerol combustion chamber; and an air flow component for combining airwith the atomized glycerol source, wherein the air flow componentincludes aerodynamic restrictions useful to provide a desired flowpattern when combined with the atomized glycerol.

A glycerol burner, such as the one described above, can be integratedinto the process reactor set-up in the present invention and used toproduce process steam (e.g., approximately 400° C.), which can then beplumbed to dedicated heat exchangers in the stream flows and to jacketedreactors to mitigate heat loss to the surroundings.

Combustion of glycerol generally proceeds according to Formula (12),

C₃H₅(OH)₃+3.5O₂→3CO₂+4H₂O+heat  (12)

and the heat of combustion is approximately 16 MJ/kg of glycerol. Thus,it is clear that combustion of glycerol requires provision of theglycerol itself, as well as a combustion-sustaining amount of oxygen(often supplied from ambient air). The prior art, however, hasheretofore failed to recognize the combination of variables that must beestablished and combined to achieve the clean and efficient combustionof glycerol and thus provide the ability to both directly withdrawglycerol as a side-stream of an industrial process and use the glycerolby-product as a fuel source for generating heat.

Generally, a standard fuel oil burner cannot easily combust glycerol dueto the high viscosity of the material. Likewise, the relatively highauto ignition temperature of glycerol also reduces the ability tocombust in a standard oil burner. Previous attempts at burning glycerolhave illustrated the associated difficulties. For example, many burnersdo not burn at a sufficiently high temperature to maintain combustion,which results in formation of sticky residues that can clog the burnerand self-extinguish the combustion. Attempts to combust glycerol using astandard fuel burning apparatus, such as a kerosene heater, have provenunsuccessful, even when trying to burn the glycerol using a continuousspark ignition source. In fact, glycerol does not evenly and efficientlycombust even in the presence of a sustained flame. This is illustratedby placing a propane torch into a glycerol spray. The glycerol in theimmediate vicinity of the propane-fed flame will burn, but there isincomplete combustion of the entire glycerol spray, and glycerol burn isnot self-sustaining after removal of the propane-fed torch. Such amethod of burning glycerol is also potentially hazardous because of thepresence of localized variations in the glycerol flowfield where theglycerol is above its thermal decomposition temperature but below itsauto-ignition temperature. Such an environment can result in theformation of undesirable species, such as acrolein.

Glycerol combustion, however, is made possible according to the methodand apparatus that is more fully described in Applicant's co-pendingU.S. Provisional Patent Application No. 60/942,290, the disclosure ofwhich is incorporated herein by reference. As such, glycerol combustionin the process of the present invention is possible by provision of anapparatus comprising a suitable glycerol combustion chamber,introduction of the glycerol into the combustion chamber in a statedesigned to maximize combustibility of the glycerol, and provision ofair via a route also designed to maximize combustibility of theglycerol.

The present invention also encompasses further processes that can beuseful for increasing conversion efficiency up to 90%, or even greater.Exemplary processes include catalyst optimization, enzymatic processes,plasma processing, and reforming of glycerol to higher-value products(e.g., propylene glycols).

In certain embodiments, the process of the present invention is carriedout as a continuous flow process. In other words, all steps in theinventive process are carried out sequentially, with the reactionproduct from the hydrolysis step (i.e., the free fatty acids) beingmoved directly into the catalytic deoxygenation step, and the reactionproduct from the catalytic deoxygenation step (i.e., the n-alkanes)being moved directly into the reforming step. Such a continuous flowprocess provides for improved energy efficiency since a single systempressurization function can be performed. If the process steps areperformed in three separate batch processes, however, three separatepressure cycles must be performed, which increases the energy input.

Hydrogen generated in the reforming step of the inventive process can beused in the catalytic deoxygenation step of the inventive process, asdescribed above. Recirculating the hydrogen product instead of disposingthe hydrogen thus further increases the energy efficiency of theprocess.

Still further, as described previously, improved catalyst performancecan also increase energy efficiency. For example, the reforming step ofthe process can result in formation of a certain content of lighthydrocarbons (LHC, e.g., C₁-C₅). Such LHC are typically not desired fortransportation fuels, such as jet fuel, diesel, and gasoline. Use ofpreferred catalysts, such as described herein, can reduce the LHCcontent. Preferably, the catalyst used in the reforming step leads to aproduced LHC content of less than about 20% by weight, based on theoverall weight of the reaction product from the reforming process. Incertain embodiments, the reforming step leads to a produced LHC contentof less than about 15% by weight, less than about 12% by weight, lessthan about 10% by weight, less than about 8% by weight, less than about5% by weight, less than about 4% by weight, less than about 3% byweight, less than about 2% by weight, or less than about 1% by weight,based on the overall weight of the reaction product from the reformingprocess.

By combining the various energy conservation steps described herein, itis possible to greatly increase the overall energy efficiency of theinventive process. For example, Table 7 below summarizes several processimprovements that can be used to increase energy efficiency. Table 7further illustrates one embodiment of the invention wherein it ispossible to realize greater than 86% efficiency for the overall processof the invention.

TABLE 7 Energy Savings Cumulative Efficiency Process EfficiencyEnhancement (kW) Energy Mass Process without energy enhancements — 71.2%72.8% Continuous flow deletes pumps at 0.22 71.5% 72.8% start ofcatalytic deoxygenation step and reforming step Burn glycerol fromhydrolysis step 0.99 72.6% 72.8% in recovery boiler and use steam toreplace heaters Burn glycerol in recovery boiler and 3.50 77.0% 72.8%use steam in jacketed reactors to eliminate heat loss Reuse recoveredH2/He in 1.68 79.2% 72.8% Reforming step so H2 energy is not wastedReuse recovered H2/He in catalytic 1.68 81.6% 72.8% deoxygenation stepso H2 energy is not wasted Implement catalyst improvements in 0.22 86.2%76.8% reforming step to reduce LHC generation to 5%

Table 7 begins with the actual efficiency of a non-optimized process, asdescribed above in relation to Table 6. However, through implementationof the various energy conservation steps described herein, it is clearlypossible to increase the overall efficiency of the inventive process toin excess of 86%. Accordingly, in specific embodiments, the process ofthe invention is useful for preparing a bio-fuel, wherein the overallprocess exhibits an energy efficiency of at least about 75%, at leastabout 80%, at least about 85%, at least about 86%, or at least about90%, wherein energy efficiency is calculated according to Formula (10).

Biofuel Characterization

Biofuels prepared according to the present invention preferably meet anumber of physical and chemical properties indicating functionalequivalence to refined hydrocarbon distillate fuel oil. In particular,volatility, freezing point, and viscosity should generally be withinspecified limits. Combustion properties of importance includeauto-ignition, energy content, and flame strength (characterized by boththe extinction strain rate and premixed laminar burning velocity).

To ensure the operational safety of jet fuels, volatility must be low.In one embodiment, volatility can be measured by the flash point, thelowest temperature at which application of a test flame causes the vaporabove the sample to ignite. Preferably, jet fuels prepared according tothe invention exhibits a flash point of at least 38° C., as required byMIL-DTL-83133E. The flash point can particularly be measured using thePensky-Martens closed cup tester (ASTM Standard Test Method D 93-00Flash Point by Tag Closed Tester). In order to meet the low volatilityrequirement, the inventive process can be carried out to preventgeneration of short alkanes (i.e., less than approximately 8 carbons)during alkane synthesis.

Due to the low temperatures associated with high altitude flightoperations, the freezing point, defined as the temperature below whichsolid hydrocarbon crystals may form, of jet fuel prepared according tothe invention should be at most −47° C. The freezing point can bemeasured using a simple manual technique following the ASTM D 2386Freezing Point of Aviation Fuels test procedure.

Viscosity can be measured using a standard reference capillaryviscometer following the test procedure called out by ASTM D 4451Kinematic Viscosity of Transparent and Opaque Liquids. Preferably, jetfuel prepared according to the invention has a viscosity of no greaterthan 8.0 mm²/s at −20° C. Such can particularly be achieved byincreasing the content of isoalkanes in the fuel product.

The auto-ignition of a fuel is a function of both the temperature andflow field. To understand the fundamental chemical kinetics, theignition temperature as a function of hydrodynamic strain rate ismeasured in a simple one-dimensional flame. In practice, the fuel isvaporized in hot nitrogen and then advected into a counterflow diffusionflame burner, flowing against a heated stream of air. The hydrodynamicstrain rate scales linearly with the fuel and oxidizer flow velocities.A stream of vaporized fuel flows against a heated stream of air at agiven temperature at an initially high strain rate. At this strain rate,the residence time is too short for chain branching reactions to occurand the fuel does not ignite. As the flow rates are decreased, thestrain rate decreases, decreasing the scalar dissipation rate,increasing the residence time, and this continues until ignitionabruptly occurs. The measurements are then repeated at a different airtemperature, building an ignition curve. The ignition curve determinedfor a biofuel prepared according to the invention can be comparedagainst ignition curves for various stocks of JP-8. The ignition curveis a strong function of the aromatic content and can be related to theCetane Index.

Another important chemical kinetic parameter is the strain rate atextinction. This is similar to the ignition strain rate-temperaturecorrelation, but a flame is ignited in a counterflow geometry at a lowstrain rate and the strain rate is incrementally increased until theflame globally extinguishes. This measurement is made as a function ofair temperature and can be compared with results for JP-8.

A third chemical kinetic parameter of importance is laminar burningvelocity, which can be measured in a combustion bomb with optical accessemploying a high-speed intensified camera. A fourth chemical parameterto be measured is the smoke point, a fundamental measure of the fuelspropensity to soot. This is important not only from an emissions viewpoint (ability of an adversary to track and target the aircraft) butalso an indirect measure of the aromatic content of the fuel.

The energy content, in kJ/kg, can be measured in a bomb calorimeterusing the ASTM D 4809 Heat of Combustion of Liquid Hydrocarbon Fuels byBomb calorimeter method. Preferably, a jet fuel prepared according tothe invention exhibits an energy content of at least about 42,800 kJ/kg.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions. Therefore, it is to be understood that theinventions are not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A process for forming a hydrocarbon compound,said process comprising: performing catalytic deoxygenation on a streamcomprising a free fatty acid by a decarboxylation reaction pathway toform a product stream comprising a paraffin.
 2. The process according toclaim 1, wherein said catalytic deoxygenation proceeds via adecarboxylation reaction pathway and a decarbonylation reaction pathway.3. The process according to claim 1, wherein said catalyticdeoxygenation comprises gas-phase deoxygenation.
 4. The processaccording to claim 1, wherein said catalytic deoxygenation comprises theuse of a fixed-bed catalyst.
 5. The process according to claim 1,wherein said catalytic deoxygenation comprises liquid-phase catalyticdeoxygenation carried out in a hydrocarbon solvent.
 6. The processaccording to claim 5, wherein the hydrocarbon solvent comprises aparaffin from the product stream.
 7. The process according to claim 1,wherein said catalytic deoxygenation is carried out at a temperature ofup to 325° C.
 8. The process according to claim 1, wherein saidcatalytic deoxygenation step comprises the use of a catalyst slurry orcatalyst dispersion.
 9. The process according to claim 1, wherein saidcatalytic deoxygenation step does not require the addition of any H₂ toremove the oxygen from the lipidic biomass.
 10. The process according toclaim 1, wherein said catalytic deoxygenation step further comprises theaddition of H₂.
 11. The process according to claim 1, wherein saidcatalytic deoxygenation is carried out in an atmosphere of about 10%volume or less H₂.
 12. The process according to claim 1, wherein theproduct stream is substantially oxygenate free.
 13. The processaccording to claim 1, wherein the conversion rate of the free fatty acidto the paraffin is at least about 90%.
 14. The process according toclaim 1, wherein the conversion rate of the free fatty acid to theparaffin is at least about 98%.
 15. The process according to claim 1,wherein the product stream comprises a paraffin having a chain length ofeight carbons or greater.
 16. The process according to claim 1, whereinthe product stream comprises a paraffin having a chain length of 10 to17 carbon atoms.
 17. The process according to claim 1, wherein theproduct stream comprises a paraffin having a chain length of 15 to 17carbon atoms.
 18. The process according to claim 1, wherein the productstream comprises heptadecane.
 19. The process according to claim 1,wherein the product stream comprises a linear paraffin.
 20. The processaccording to claim 1, wherein the paraffin has a carbon number that isone less than the free fatty acid.
 21. The process according to claim 1,wherein the free fatty acid has 12 carbon atoms or greater.
 22. Theprocess according to claim 1, wherein the free fatty acid has 12 to 18carbon atoms.
 23. The process according to claim 1, wherein the freefatty acid comprises stearic acid, linoleic acid, linolenic acid,palmitic acid, or oleic acid.
 24. The process according to claim 1,wherein the process excludes cracking.
 25. The process according toclaim 1, wherein said deoxygenation is carried out in the presence of anoble metal catalyst.
 26. The process according to claim 25, whereinsaid noble metal catalyst comprises palladium.
 27. The process accordingto claim 25, wherein said catalyst comprises a carbon support.
 28. Theprocess according to claim 1, further comprising performing thermalhydrolysis on a lipidic biomass to form the free fatty acid stream. 29.The process according to claim 28, wherein said thermal hydrolysiscomprises heating the lipidic biomass in the presence of water to atemperature of about 220° C. to about 300° C. under a pressuresufficient to prevent the water in the reactor from flashing to steam.